| 54 | order |
| 398 | orbit |
| 451 | original |
| 547 | organism |
| 727 | origin |
| 839 | organic |
| 873 | ordinary |
| 925 | organize |
| 1025 | organ |
| 1805 | originate |
| 2339 | oral |
| 2401 | organization |
| 2427 | orientation |
| 3108 | orchestra |
| 2568 | oscillation |
| 940 | otherwise |
| 444 | outside |
| 1011 | outer |
| 1051 | output |
| 1498 | outcome |
| 1862 | outbreak |
| 2175 | outline |
| 2406 | outward |
| 2600 | outstanding |
| 2618 | outfit |
| 2935 | outlet |
| 3035 | outlook |
| 3098 | outdoor |
| 966 | overall |
| 1582 | overcome |
| 1905 | overseas |
| 2140 | overwhelm |
| 2313 | oven |
| 2402 | overlap |
| 2457 | overlook |
| 3127 | oval |
| 3209 | overhaul |
| 3218 | overload |
| 1198 | owner |
| 2550 | owe |
| 422 | oxygen |
| 771 | oxide |
| 2495 | oxidize |
| 2576 | oxidation |
| 440 | ozone |
