(US, slang, street slang) The police.

(British, navy) First Officer.

A selective service class denoting that the registrant is only available for noncombat military service due to their conscientious objector status

A selective service class denoting that the registrant a conscientious objector available for alternate service contributing to maintenance of national health, safety, or interest.

plural of o-scope

(electronics, informal) oscilloscope

(medicine) Initialism of rule out: used to indicate that a certain possible diagnosis should be considered, and appropriate tests performed to rule it out.

Alternative form of billy-oh

(Australia and New Zealand colloquial, now historical) Someone who sells rabbits for food, especially an itinerant salesman.

(informal) standing ovation