This page lists 34 first aid words that start with O, ranging from “Oxygen” to “Outer Bandage Layer.” The entries cover emergencies, equipment, assessment tools, and wound care techniques used in real response situations. You’ll find terms from standard first aid training alongside concepts from advanced emergency medical practice.
First aid words are terms used to describe injuries, conditions, equipment, and actions in emergency and pre-hospital care. Antoine Lavoisier coined the word “oxygen” in 1777; today it is the single most critical element in nearly every first aid scenario. These terms help responders and bystanders communicate quickly and accurately when time is critical.
Below you’ll find the table with Word, Definition, and Description.
Word: Each entry names a first aid term starting with O; use it to quickly identify the concept you need.
Definition: This gives you a concise medical or procedural explanation of what each word means in clear, everyday language.
Description: This explains how each term applies in practice, including what to do, what to watch for, and why it matters.
First aid words
| Word | Definition |
|---|---|
| Oxygen | A colorless, odorless gas essential for cellular respiration and life |
| Overdose | A toxic amount of a substance — drug, medication, or chemical — that harms the body |
| Open Fracture | A broken bone that punctures through the skin, creating an external wound |
| Open Wound | Any break in the skin’s surface that exposes underlying tissue |
| Oropharyngeal Airway | A curved plastic device inserted into the mouth to keep the airway open |
| Occlusive Dressing | An airtight, waterproof bandage that seals a wound from air and contaminants |
| Oxygen Saturation | The percentage of hemoglobin molecules in the blood carrying oxygen |
| OPQRST | A mnemonic used to assess a patient’s pain or symptoms: Onset, Provocation, Quality, Radiation, Severity, Time |
| Oral Rehydration | The replacement of fluids and electrolytes by drinking rather than intravenous infusion |
| Obstruction | A blockage that prevents normal passage, especially in the airway or blood vessels |
| Open Chest Wound | A penetrating injury that breaches the chest wall and may allow air into the pleural space |
| Opioid | A class of drugs — including morphine, heroin, and fentanyl — that bind opioid receptors to relieve pain |
| Opioid Overdose | A medical emergency caused by excessive opioid use, leading to respiratory depression |
| Organophosphate Poisoning | Toxic exposure to organophosphate compounds that inhibit acetylcholinesterase, disrupting nerve signals |
| Oral Glucose | A fast-acting sugar gel or solution given by mouth to raise dangerously low blood sugar |
| Overexposure | Prolonged or excessive contact with a harmful environmental or chemical agent |
| Overheating | A condition where the body’s core temperature rises to a dangerous level |
| Orthostatic Hypotension | A drop in blood pressure that occurs when a person stands up quickly |
| Oxygen Therapy | The medical administration of supplemental oxygen above atmospheric concentrations |
| Oxygen Mask | A device worn over the nose and mouth to deliver supplemental oxygen from a supply source |
| Oxygen Cylinder | A pressurized metal tank containing medical-grade oxygen for therapeutic use |
| Open Pneumothorax | Air entering the pleural space through an open chest wound, causing lung collapse |
| Oropharynx | The middle section of the throat connecting the mouth to the lower airway |
| Onset | The point in time when symptoms or an injury first began |
| Organ Failure | The loss of normal function in a vital organ such as the heart, kidneys, or liver |
| Orthopnea | Difficulty breathing that worsens when lying flat, relieved by sitting or standing |
| Otitis Media | An infection or inflammation of the middle ear |
| Otalgia | Ear pain, which may arise from infection, injury, pressure changes, or referred pain |
| Output (Urinary) | The volume of urine produced over a period of time, used as an indicator of hydration and organ function |
| OTC Medication | Over-the-counter medicine available without a prescription, such as pain relievers or antihistamines |
| On-Scene Safety | The assessment of a scene for hazards before approaching to provide care |
| Occluded Vessel | A blood vessel that is partially or fully blocked, restricting blood flow |
| Orthopedic Injury | Damage to any component of the musculoskeletal system including bones, joints, ligaments, or tendons |
| Outer Bandage Layer | The outermost wrap applied over wound dressings to secure and protect them |
Descriptions
Oxygen
The most critical element in first aid; supplemental oxygen is delivered to patients in respiratory distress, shock, or cardiac arrest to support vital organ function.
Overdose
A medical emergency where too much of a substance overwhelms the body; symptoms range from unconsciousness to respiratory failure. Call emergency services immediately.
Open Fracture
Also called a compound fracture, this injury carries high infection risk. First aid involves covering the wound with a sterile dressing without pushing the bone back in.
Open Wound
Open wounds include cuts, lacerations, abrasions, and punctures. First aid focuses on controlling bleeding, cleaning the wound, and applying a sterile bandage.
Oropharyngeal Airway
Commonly called an OPA, this device prevents the tongue from blocking the throat in an unconscious patient. It is used by trained responders alongside other airway management.
Occlusive Dressing
Primarily used for penetrating chest wounds to prevent air from entering the chest cavity, which could cause a life-threatening pneumothorax.
Oxygen Saturation
Measured with a pulse oximeter clipped to a finger; normal levels are 95–100%. Readings below 90% indicate hypoxia and signal a need for supplemental oxygen.
OPQRST
A structured questioning tool used in first aid and emergency medicine to gather a complete picture of a patient’s complaint quickly and systematically.
Oral Rehydration
Used for mild to moderate dehydration from diarrhea, vomiting, or heat exposure. Oral rehydration salts (ORS) solutions are the preferred first-line treatment worldwide.
Obstruction
Airway obstruction is a top first aid emergency; rescue techniques like back blows and abdominal thrusts aim to dislodge the blocking object and restore breathing.
Open Chest Wound
Treated by applying a chest seal or vented occlusive dressing to prevent tension pneumothorax, a rapidly life-threatening condition.
Opioid
Opioids can cause life-threatening respiratory depression in overdose. Naloxone (Narcan) is the emergency antidote and can be administered by bystanders.
Opioid Overdose
Signs include slow or stopped breathing, pinpoint pupils, and unresponsiveness. Naloxone reverses the overdose and rescue breathing may be required while awaiting help.
Organophosphate Poisoning
Found in certain pesticides and nerve agents; causes excessive secretions, muscle weakness, and seizures. Remove the patient from exposure and seek emergency care immediately.
Oral Glucose
Used in first aid for conscious diabetic patients experiencing hypoglycemia. It is placed inside the cheek to be absorbed quickly; never give orally to an unconscious person.
Overexposure
Includes sunburn, heat exhaustion, cold injury, or chemical exposure. First aid involves removing the person from the source and treating resulting symptoms.
Overheating
Also called hyperthermia; ranges from heat cramps to heat stroke. Cool the person rapidly by removing excess clothing, applying cool water, and fanning.
Orthostatic Hypotension
Can cause dizziness or fainting; relevant in first aid when a patient collapses after rising. Lay the patient flat and elevate the legs to improve blood flow to the brain.
Oxygen Therapy
Used in first aid for hypoxia, respiratory distress, carbon monoxide poisoning, shock, and many other emergencies. Delivered via mask, nasal cannula, or bag-valve mask.
Oxygen Mask
Non-rebreather masks can deliver up to 90% oxygen concentration and are standard equipment in advanced first aid and emergency medical response.
Oxygen Cylinder
Portable cylinders allow first responders to administer oxygen in the field. They come in various sizes; responders must check pressure gauges to ensure adequate supply.
Open Pneumothorax
A life-threatening emergency; first aid involves sealing the wound with a vented chest seal. The patient requires urgent surgical intervention.
Oropharynx
A critical airway structure; maintaining its openness is a core first aid priority, especially in unconscious patients where the tongue may fall back and obstruct it.
Onset
Recording onset is critical in patient history taking. Knowing whether symptoms started suddenly or gradually helps rescuers and medics identify the cause.
Organ Failure
Can result from trauma, infection, or lack of oxygen. First aid focuses on maintaining circulation and breathing while emergency services are contacted.
Orthopnea
A symptom often seen in heart failure or severe asthma. In first aid, placing the patient in an upright position helps ease breathing while awaiting advanced care.
Otitis Media
Not a first aid emergency in most cases, but severe cases with high fever or dizziness in children may warrant urgent care. Pain management and medical evaluation are recommended.
Otalgia
Can indicate a perforated eardrum or ear infection. First aid includes keeping the ear dry and seeking medical evaluation; do not insert objects into the ear canal.
Output (Urinary)
Decreased urine output can signal dehydration or shock. In first aid, monitoring output helps assess whether a patient’s condition is improving or deteriorating.
OTC Medication
Relevant in first aid for managing fever, allergic reactions, and minor pain. Responders should ask patients about OTC use to avoid drug interactions.
On-Scene Safety
The first step in any first aid response; rescuers must confirm the area is safe from traffic, fire, chemicals, or violence before rendering aid.
Occluded Vessel
Occurs in heart attacks and strokes. First aid focuses on keeping the patient calm, monitoring vitals, and activating emergency services immediately.
Orthopedic Injury
Common in trauma and sports injuries. First aid follows the RICE protocol — Rest, Ice, Compression, Elevation — and immobilization to prevent further damage.
Outer Bandage Layer
Typically an elastic or conforming bandage; it holds dressings in place, provides light compression, and protects the wound from external contamination.