| TERM | MEANING |
| obstetr/o | midwife |
| octa-, octi- | eight |
| ocul/o | eye |
| odont/o | tooth |
| -oid | resembling |
| -ole | little, small |
| ole/o | oil |
| olfact/o | smell |
| olig/o | scanty, few, little |
| -oma | tumor, mass |
| om/o | shoulder |
| omphal/o | navel |
| onc/o | tumor, mass |
| onych/o | nail |
| o/o | egg, ovum |
| oophor/o | ovary |
| ophry/o | eyebrow |
| ophthalm/o | eye |
| -opia, -opsia | vision |
| opisth/o | backward, behind |
| op/o | juice, face |
| -opsy | to view |
| opt/o | eye, vision |
| orch/o, orchi/o, orchid/o | testis |
| -orexia | appetite |
| organ/o | organ |
| ornith/o | bird |
| or/o | mouth |
| orth/o | straight, normal, correct |
| osche/o | scrotum |
| oscill/o | to swing |
| -osis | condition, status, abnormal increase |
| osm/o, osmia | sense of smell, odor, impulse |
| osphresi/o, -osphresia | sense of smell, odor |
| oste/o | bone |
| ot/o | ear |
| ovari/o | ovary |
| ov/o, ov/i | egg, ovum |
| ox/o, -oxia | oxygen |
| oxy- | sharp, quick, sour |
