| OAS | old age security; oral allergy syndrome; osmotically active substance |
|---|---|
| OASD | ocular albinism-sensorineural deafness [syndrome] |
| OASDHI | Old Age, Survivors, Disability and Health Insurance |
| OASDI | Old Age Survivors and Disability Insurance |
| OASI | Old Age and Survivors Insurance |
| OASP | organic acid soluble phosphorus |