| OPM | occult primary malignancy; Office of Personnel Management; ophthalmoplegic migraine |
|---|---|
| OPRR | Office of Protection from Research Risks |
| OPSR | Office of Professional Standards Review |
| ORDS | Office of Research, Demonstration, and Statistics |
| OS | left eye [Lat. oculus sinister]; occipitosacral; occupational safety; office surgery; Omenn syndrome... |