| ON | occipitonuchal; office nurse; onlay; optic nerve; orthopedic nurse; osteonecrosis; osteonectin; over... |
|---|---|
| OPHC | Office of Prepaid Health Care |
| OPM | occult primary malignancy; Office of Personnel Management; ophthalmoplegic migraine |
| OPRR | Office of Protection from Research Risks |
| OPSR | Office of Professional Standards Review |