| NOS | network operating system; nitric oxide synthetase; non-organ-specific; not on staff; not otherwise s... |
|---|---|
| OAR | organ at risk |
| OBF | organ blood flow |
| OC | obstetrical conjugate; occlusocervical; office call; on call; only child; optic chiasma; oral contra... |
| OPO | Organ Procurement Organization |