Here you’ll find 26 Prefixes that start with O, organized from “ob-” to “oxy-“. These prefixes often come from Latin or Greek and help with word-building, vocabulary study, and reading technical terms. Entries prioritize common, high-utility prefixes first, then technical forms, and include origins plus clear examples.
Prefixes that start with O are short meaningful elements added to word stems to alter or refine their sense. Many derive from Latin and Greek, and “oxy-” appears in “oxygen”, named during 18th-century chemical discoveries.
Below you’ll find the table with Prefix, Origin, Meaning, Examples, and Notes.
Prefix: Shows the prefix itself so you can quickly identify its spelling and common forms for use.
Origin: Gives the linguistic source so you understand historical roots and related forms across languages.
Meaning: Provides a concise definition (three to seven words) so you grasp the prefix’s basic sense at a glance.
Examples: Lists two to four clear words using the prefix so you see real usage and learn word-building.
Notes: Includes brief usage tips, variations, and links so you can explore exceptions or technical meanings further.
Prefixes that start with O
| Prefix | Origin | Meaning | Example words |
|---|---|---|---|
| ob- | Latin (ob) | against; in the way; toward | object; obstruct; oppose; occur |
| octa- | Greek (oktō) and Latin (octo) | eight | octagon; octopus; October; octet |
| oculo- | Latin (oculus) | relating to the eye | oculist; oculomotor; binocular |
| odonto- | Greek (odous, odontos) | relating to teeth | odontology; orthodontist; periodontics |
| odyno- | Greek (odynē) | pain | odynophagia; odynometer |
| oeno- | Greek (oinos) | relating to wine | oenology; oenophile; oenology |
| oiko- | Greek (oikos) | house; household; dwelling | ecology; economy; ecumenical |
| oleo- | Latin (oleum) | relating to oil | oleograph; oleoresin; oleomargarine |
| oligo- | Greek (oligos) | few; little; small | oligarchy; oligopoly; oligocene |
| omni- | Latin (omnis) | all; every; everywhere | omniscient; omnivore; omnipresent |
| onco- | Greek (onkos) | tumor; mass; bulk | oncology; oncogene; oncovirus |
| onto- | Greek (on, ontos) | being; existence | ontology; ontogeny; ontologic |
| onycho- | Greek (onyx, onykhos) | nail; claw | onychomycosis; onychophagy |
| oo- | Greek (ōion) | egg; ovum | oocyte; oogenesis; oology |
| oophoro- | Greek (ōophoron) | relating to the ovary | oophorectomy; oophoritis |
| ophthalmo- | Greek (ophthalmos) | relating to the eye | ophthalmology; ophthalmologist; ophthalmoscope |
| opistho- | Greek (opisthen) | behind; at the back; backward | opisthobranch; opisthosoma |
| organo- | Greek (organon) | organ; organic chemical compound | organometallic; organophosphate; organogenesis |
| ornitho- | Greek (ornis, ornithos) | relating to birds | ornithology; ornithopter; ornithomancy |
| oro- | Greek (oros) | mountain | orography; orogeny; orology |
| oro- | Latin (os, oris) | mouth | orofacial; oronasal; oral |
| ortho- | Greek (orthos) | straight; correct; right | orthodox; orthodontist; orthopedic |
| osmo- | Greek (osmē) | odor; smell | osmia; osmology |
| osteo- | Greek (osteon) | relating to bones | osteoporosis; osteopath; osteoarthritis |
| oto- | Greek (ous, otos) | relating to the ear | otology; otoscope; otitis |
| oxy- | Greek (oxys) | sharp; acid; pointed; keen | oxygen; oxymoron; oxyacetylene |
Descriptions
ob-
A versatile prefix indicating opposition or movement toward. It often changes form, becoming oc-, of-, or op- before certain consonants.
octa-
Used for the number eight. October was the eighth month in the original Roman calendar, which began in March.
oculo-
The Latin-derived prefix for “eye,” often used in general and anatomical terms. Compare with the Greek-derived ophthalmo-.
odonto-
The standard prefix for anything related to teeth, forming the basis of many dental and medical specializations.
odyno-
A medical prefix used to denote pain, particularly pain that occurs when swallowing (odynophagia).
oeno-
Used in words concerning wine and winemaking. An oenophile is a connoisseur or lover of wine. Also spelled eno-.
oiko-
Forms words related to the house or environment. ‘Economy’ originally meant household management, while ‘ecology’ is the study of the house of nature.
oleo-
Indicates a connection to oil. An oleograph is a print textured to look like an oil painting.
oligo-
Used in science and politics to describe a state of having “few” or “little” of something, like an oligarchy (rule by the few).
omni-
A popular and powerful prefix signifying “all.” An omnivore eats all things (both plants and animals), and an omniscient being knows all things.
onco-
A key prefix in medicine referring to tumors and cancer. Oncology is the branch of medicine that specializes in treating cancer.
onto-
A philosophical and scientific prefix dealing with the nature of being or existence. Ontology is a major branch of metaphysics.
onycho-
A medical prefix for conditions related to the fingernails or toenails, such as onychomycosis (a fungal nail infection).
oo-
A biological prefix used for words related to eggs or ova. An oocyte is an immature egg cell in an ovary.
oophoro-
A specific medical prefix for the ovary, literally meaning “egg-bearing.” An oophorectomy is the surgical removal of an ovary.
ophthalmo-
The primary prefix for the eye in medical and scientific terminology. Compare with the more general Latin-derived oculo-.
opistho-
An anatomical prefix indicating a position at the back or rear of a body part.
organo-
Used in biology for organs and in chemistry for compounds containing carbon, especially when bonded to metal (organometallic).
ornitho-
The definitive prefix for all things related to birds. Ornithology is the scientific study of birds.
oro-
Used in geology and geography for terms related to mountains. Orogeny refers to the process of mountain formation.
oro-
An anatomical prefix for the mouth. It is distinct from the Greek prefix oro- meaning “mountain.”
ortho-
A very common prefix used to mean correct, straight, or upright, from religious belief (orthodox) to teeth straightening (orthodontics).
osmo-
Refers to the sense of smell. This is less common than the other osmo- related to pressure, which comes from a different root.
osteo-
The fundamental medical prefix for bones. Osteoporosis is a well-known condition where bones become weak and brittle.
oto-
The standard medical and scientific prefix for the ear. An otoscope is the instrument a doctor uses to look inside your ear.
oxy-
Has two main senses: “sharp” as in oxymoron (“sharp-dull”) and “acid” or “containing oxygen” as in oxygen (“acid-former”).