| NR | do not repeat [Lat. non repetatur]; nerve root; neural retina; neutral red; noise reduction; nonreac... |
|---|---|
| OR | a logical binary relation that is true if any argument is true, and false otherwise; [o]estrogen rec... |
| O-R | oxidation-reduction |
| OR&F | open reduction and fixation |
| ORP | oxidation-reduction potential |