| OER | osmotic erythrocyte [enrichment]; oxygen enhancement ratio |
|---|---|
| OP | occipitoparietal; occipitoposterior; occiput posterior; octapeptide; olfactory peduncle; opening pre... |
| OPP | osmotic pressure of plasma; oxygen partial pressure |
| OROS | oral osmotic |
| osm | osmole; osmosis, osmotic |