| NACSAP | National Alliance Concerned with School-Age Parents |
|---|---|
| OA | obstructive apnea; occipital artery; occipito-anterior; occiput anterior; octanoic acid; ocular albi... |
| OAA | Old Age Assistance; Older Americans Act; Opticians Association of America; oxaloacetic acid |
| OAB | ABO blood group; old age benefits |
| OAS | old age security; oral allergy syndrome; osmotically active substance |