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(ō-pāk′) [L. opacus, dark] 1. Impenetrable by visible light rays or by other forms of radiant energy such as x-rays. 2. Not transparent or translucent.


outpatient parenteral antibiotic therapy.


[AS.] 1. Not closed. 2. Uncovered or exposed, as a wound to air. 3. To puncture, as to open a boil. 4. Interrupted, as in an electric circuit when current cannot pass because a switch is open. 5. In traumatic injury, a synonym for “penetrating.”

open bite

SEE: under bite.

open enrollment

SEE: open enrollment period.


(ō′pĕ-ning) 1. The act of making or becoming open. 2. A hole, aperture, entrance, or open space.

aortic o. Hiatus aorticus

pelvic o. Pelvic brim.

pyloric o. The opening between the stomach and duodenum.

opening snap

An abnormal early diastolic extra heart sound usually associated with stenosis of one of the atrioventricular valves. Most commonly, the sound reflects mitral valve stenosis. The brief, high-pitched snapping sound is unaffected by respiration and is heard best between the apex and the lower left sternal border.


Attentiveness, interest in new experiences, inquisitiveness, or receptivity to change.

open notes

Granting patients access to their medical records and clinician encounters. The process is facilitated by giving patients the ability to sign in to their electronic health records.

open set speech recognition

The ability to understand spoken language without using visible cues.


(ŏp′ĕr-ă-bl) [L. operor, to work] 1. Practicable. 2. Subject to treatment by surgery with reasonable expectation of cure, palliation, or improvement.


(ŏp″ĕr-ănt) Producing effects.

operant conditioning

SEE: operant conditioning.


(ŏp′ĕr-āt) [L. operatus, worked] To perform a surgical procedure.


(op″ĕ-rā′shŏn) [L. operatio, a working] 1. The act of operating. 2. A surgical procedure. 3. The effect or method of action of any type of therapy. SEE: surgery.


(op″ĕ-rā′shŏn-ĕl) 1. In active or routine use. 2. Practical.


(ŏp′ĕr-ă-tĭv) [L. operativus, working] 1. Effective, active. 2. Pert. to or brought about by an operation.

operative dentistry

SEE: dentistry, operative.

operator dependent

(op″ĕ-rā′tÄĕr dē-pÄĕn′dÄĕnt) Influenced by variations in ...

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