This list includes 49 Legal terms that start with O, from “Oath” to “Ownership”. These entries focus on established legal vocabulary used across statutes, case law, and everyday practice, and they support study, drafting, and research.
Legal terms that start with O are concise legal labels used to identify doctrines, procedures, and rights beginning with “O”. Many trace to Latin or Old English, and “oath” remains a vivid courtroom ritual example.
Below you’ll find the table with Term, Definition, Etymology, Jurisdiction, Usage/Example, Related Terms, and Notes.
Term: The headword itself; you use it to locate and recognize the legal entry quickly in study or research.
Definition: A concise legal meaning in one or two sentences; you rely on it for quick comprehension and exam review.
Etymology: Brief origin and root language; you use it to understand the historical context and subtle meanings.
Jurisdiction: Notes where the term is used or varies; you check this to apply the term correctly across different legal systems.
Usage/Example: A short illustrative sentence or context showing how the term appears in practice or litigation.
Related Terms: Cross-references to connected entries; you follow these to expand understanding or find narrower and broader concepts.
Notes: Supplementary details, statutory citations, or editorial comments; you use these for further research and deeper reading.
Legal terms that start with O
| Term | Definition | Type | Jurisdiction |
|---|---|---|---|
| Oath | Formal sworn promise to tell truth or perform duties. | Procedure | Universal |
| Oath of office | Sworn pledge by an official to perform duties lawfully. | Procedure | Universal |
| Obiter dictum | Judicial remark not essential to the decision. | Doctrine | Common law (US, UK, Commonwealth) |
| Objection | Formal challenge during proceedings to exclude evidence or argument. | Procedure | Common law |
| Obligation | Legal duty to act or refrain from acting. | Concept | Civil and common law |
| Obligation of means | Duty to take reasonable care, not guarantee results. | Doctrine | Civil law jurisdictions |
| Obligation of result | Duty to achieve a specified outcome, not just effort. | Doctrine | Civil law jurisdictions |
| Obligee | Person entitled to performance under an obligation. | Noun/party | Civil and common law |
| Obligor | Person who owes a duty or performance to another. | Noun/party | Civil and common law |
| Obscenity | Material legally banned for sexual offensiveness lacking value. | Substantive law | US, UK, other jurisdictions |
| Obstruction of justice | Crime of interfering with legal or investigatory processes. | Offense | US, UK, common law |
| Offence/Offense | Act punishable under criminal law. | Offense | Universal (spellings vary) |
| Offer | Proposal to contract on specified terms. | Contract term | Common law |
| Offeree | Person to whom an offer is made. | Noun/party | Common law |
| Offeror | Person who makes an offer. | Noun/party | Common law |
| Officer | Person holding a position of trust or authority. | Role | Universal |
| Official immunity | Legal protection for officials acting within authorized duties. | Doctrine | US, UK, common law |
| Official misconduct | Crime or tort involving abuse of official position. | Offense | US, UK, common law |
| Officious intermeddler | Person who confers benefit without legal right to restitution. | Doctrine | Common law (equity) |
| Omission | Failure to act where law imposes a duty to act. | Element/Conduct | Criminal and civil law |
| Onus | Burden of proof or duty of persuasion. | Evidentiary term | Common law |
| Open court | Principle that judicial proceedings be public and transparent. | Principle | Common law (US, UK) |
| Open meetings law | Statutes requiring public agency meetings to be open to public. | Statute | US (and others) |
| Open records law | Rules granting public access to government documents. | Statute | US, many jurisdictions |
| Operating agreement | Contract governing members’ relations in an LLC. | Document/contract | US (LLC law) |
| Opinion | Court’s written explanation of its ruling. | Judicial instrument | Common law |
| Opinion evidence | Testimony that expresses a witness’s belief or inference. | Evidence | Common law |
| Opinio juris | State belief that an action is legally obligatory in international law. | Doctrine | International law |
| Opposition | Administrative challenge to a pending intellectual-property application. | Procedure | Patent/trademark law (international) |
| Oppression | Conduct unfairly prejudicial to shareholders warranting remedy. | Remedy/statute | UK, Canada, Australia |
| Option | Contract right to buy or sell property at set terms. | Contract/property | Common law |
| Opt-out | Formal rejection of participation or consent in a legal scheme. | Procedure/consumer law | US, EU |
| Ordinary course of business | Standard commercial conduct in business operations. | Commercial standard | Common law |
| Ordinance | Local law enacted by municipal authority. | Statute/local law | US, UK, municipalities |
| Organic law | Fundamental laws establishing institutions, often constitutions. | Constitutional concept | Various jurisdictions |
| Original jurisdiction | Court’s power to hear a case first, not on appeal. | Jurisdictional term | Worldwide courts |
| Originalism | Judicial philosophy interpreting texts as originally intended. | Jurisprudence theory | Primarily US constitutional law |
| Originality | Requirement that a work be independently created for copyright. | IP law concept | Copyright law (US, UK, EU) |
| Orphan works | Copyrighted works whose owners cannot be located or identified. | IP policy term | US, EU, international |
| Ostensible authority | Apparent authority that a third party reasonably perceives in an agent. | Agency doctrine | Common law |
| Ouster | Removal of person from possession of property or office. | Remedy/procedure | Common law |
| Ouster clause | Statutory provision attempting to exclude judicial review. | Statute | UK, Australia, other common law |
| Out-of-court statement | Assertion made outside courtroom, often hearsay material. | Evidence doctrine | Common law |
| Overbreadth doctrine | Rule striking laws that prohibit substantially protected expression. | Constitutional doctrine | US |
| Overriding royalty | Nonworking royalty interest in mineral or lease rights. | Property/royalty | US oil and gas law |
| Overt act | Open action in furtherance of a conspiracy. | Criminal element | US, UK, common law |
| Own recognizance | Release from custody on personal promise to appear without bail. | Pretrial release | US, common law |
| Ownership | Legal right of possession, use, and disposition of property. | Property right | Universal |
| Owner | Person or entity holding legal title or control over property. | Noun/party | Universal |
Descriptions
Oath
From Old English “āð”; a formal solemn promise used in court or office to ensure truthful testimony or faithful duty performance.
Oath of office
Ceremonial oath deriving from Anglo-Latin practice; binds public officers to constitutional or statutory duties.
Obiter dictum
Latin for “said by the way”; persuasive but not binding commentary in judicial opinions.
Objection
From Latin objicere; a courtroom device to preserve issues for appeal and control trial evidence.
Obligation
From Latin obligatio; central contract and tort concept denoting enforceable duties between parties.
Obligation of means
Civil-law concept (obligation de moyens) from Latin roots; contrasts with result obligations in contracts and professional duties.
Obligation of result
(Obligation de résultat) Latin-rooted civil-law idea requiring promised outcomes, common in sale or turnkey contracts.
Obligee
From Latin obligare; the party who benefits from an obligation, often used in contract and surety contexts.
Obligor
From Latin obligare; the party bound to perform under a contract or debt.
Obscenity
From Latin obscenus; regulated under criminal and censorship laws (e.g., U.S. Miller test for obscenity).
Obstruction of justice
From Latin obstruere “to block”; covers acts like destroying evidence or impeding investigations.
Offence/Offense
From Old French; denotes crimes or statutory violations—spelling varies by jurisdiction (UK “offence”, US “offense”).
Offer
From Old English ofer; foundational in contract formation when accepted by the offeree.
Offeree
Party who may accept or reject an offer; term traces to offer + -ee agentive suffix.
Offeror
The proposing party in contract negotiations; older dictionaries also use “offeror” or “offeror”.
Officer
From Latin officium “duty”; applies to public officers, corporate officers, and law enforcement roles.
Official immunity
Doctrine from medieval office concepts; shields some public acts from liability, subject to limits.
Official misconduct
Covers corrupt or wrongful acts by officials; statutory definitions vary by jurisdiction.
Officious intermeddler
Latin-rooted phrase; equity denies recovery to unwarranted volunteers, used in unjust enrichment analysis.
Omission
From Latin omittere; criminal liability may arise from omissions when statute or relationship creates duty.
Onus
Latin “onus” meaning burden; used interchangeably with “burden” in evidence and procedure contexts.
Open court
Rooted in older English practice; supports public access to trials and records, tied to due process.
Open meetings law
Also called “sunshine laws”; aim to ensure government transparency and public participation.
Open records law
Freedom-of-information-type laws (e.g., FOIA) deriving from transparency principles.
Operating agreement
From business practice; sets management, profit sharing, and governance for limited liability companies.
Opinion
From Latin opinio; explains legal reasoning, precedential value varies (majority, concurring, dissent).
Opinion evidence
Distinguishes lay vs expert opinion; rules limit speculative or improper opinion testimony.
Opinio juris
Latin “opinio juris sive necessitatis”; key element of customary international law formation.
Opposition
Used in patent and trademark offices to contest applications during administrative proceedings.
Oppression
Company law term for equitable remedies against oppressive corporate conduct; statutory remedies vary.
Option
From Latin optio; widely used in real estate, securities, and commercial contracts to secure choice.
Opt-out
Common in privacy, class actions, and regulatory schemes; means a person declines inclusion.
Ordinary course of business
Phrase used in contract, bankruptcy, and fiduciary contexts to judge routine versus extraordinary actions.
Ordinance
From Latin ordinare; regulates local matters subject to state or national law limits.
Organic law
Term for basic governing law; may refer to constitutions or foundational statutes.
Original jurisdiction
From Latin originalis; contrasts with appellate jurisdiction and determines venue and forum.
Originalism
Contemporary theory rooted in textualism and historical interpretation of constitutional meaning.
Originality
From Latin originalis; central to copyright and some aspects of patent novelty.
Orphan works
Term arises in copyright policy debates over access and licensing when rights-holders are unidentifiable.
Ostensible authority
From Latin ostendere “to show”; binds principals to agents’ acts when authority appears real to outsiders.
Ouster
From Old French “oster” to remove; used in property disputes and actions seeking possession.
Ouster clause
Clause purporting to limit courts’ oversight; often scrutinized or struck down to protect rule of law.
Out-of-court statement
Relevant to hearsay rules; admissibility depends on exceptions and reliability.
Overbreadth doctrine
Developed in First Amendment law to prevent laws that sweep in lawful speech.
Overriding royalty
A contract-based interest in production revenue, common in energy and mineral law.
Overt act
Overt from Latin aperire “open”; used to link conspirators by an observable step toward crime.
Own recognizance
Often shortened “released on own recognizance”; reflects trust in defendant’s promise to return.
Ownership
From Old English “āgen”; core property law concept denoting bundle of rights in assets.
Owner
Holder of ownership rights; term used across property, corporate, and contract contexts.