| OCLI |
| oclock |
| OCO |
| Ocoee |
| Oconnor |
| Oconomowoc |
| Ocotea |
| Ocotillo |
| OCR |
| ocracy |
| ocreaceous |
| ocreae |
| ocreated |
| OCS |
| oct- |
| octa- |
| octachordal |
| octachronous |
| octactinal |
| octactine |
| octad |
| octadecahydrate |
| octadecyl |
| octadic |
| octads |
| octaechos |
| octaeteric |
| octaeterid |
| octagonal |
| octagonally |
| octahedral |
| octahedrally |
| octahedrite |
| octahedroid |
| octahedrous |
| octahydrate |
| octal |
| octamerism |
| octan |
| octanaphthene |
| octandrious |
| octane |
| octangles |
| octangular |
| octanols |
| Octans |
| octants |
| octapeptide |
| octaploidy |
| octaploidic |
| octarch |
| octarchy |
| octarius |
| octaroon |
| octastich |
| octastichon |
| octastylos |
| octastrophic |
| octavalent |
| octavaria |
| Octave |
| octaves |
| octavic |
| Octavie |
| Octavla |
| octavo |
| octdra |
| octect |
| octene |
| octennial |
| octets |
| octette |
| octyl |
| octile |
| octillions |
| octillionth |
| octyne |
| octingentenary |
| octoalloy |
| octoate |
| octobers |
| octobrachiate |
| octocentennial |
| octochord |
| Octocorallia |
| octocoralline |
| octodactyle |
| octodactylous |
| octodecillions |
| octodecillionth |
| octodecimos |
| octodentate |
| octodont |
| occasioned |
| occasionings |
| occasionless |
| Occident |
| Occidental |
| Occidentalised |
| Occidentalising |