| Abbreviation | Definition |
|---|---|
| OBS | obstructive bowel syndrome |
| OBS | obvious bullshit |
| OBS | oligoclonal bands |
| OCAIRS | Occupational Circumstances Assessment Interview and Rating Scale |
| OCCO | Office of the Chief Clinical Officer |
| OCMO | Office of the Chief Medical Officer (Wales) |
| OCN | oculomotor nucleus |
| OCN | optically clear nuclei |
| OCN | osteocalcin |
| OCU | observation care unit |
| OCU | Occupational Command Unit |
| OD | occupational dermatitis |
| OD | Organ Dysfunction |
| ODA | on day of admission |
| ODA | Operating Department Assistant |
| ODA | Orphan Drug Act |
| ODA | outer dynein arm |
| ODA | Overseas Development Agency |
| ODA | Overseas Doctors Agency |
| ODP | ocular dominance plasticity |