- Opiate Adj Noun Verb
- Opine Verb
- Opportune Adj Verb
- Oppose Verb Pres. Participle Past Participle Noun
- Oppress Verb
- Oppugn Verb Past Participle Pres. Participle
- Opsonize Verb
- Opt Verb
- Opt in Verb
- Opt out Verb
- Optate Verb
- Optimise Verb
- Optimize Verb
- Option Noun Verb Adj
- Oracle Noun Verb Pnoun Adj
- Orange Adj Noun Verb
- Orate Verb
- Orb Noun Verb Adj
- Orbit Noun Verb Adj Pres. Participle Past Participle
- Orchestrate Verb Past Participle Pres. Participle
- Ordain Verb
- Ordeal Noun Verb
- Order Noun Verb Adj Past Participle
- Ordinate Adj Noun Verb
- Organise Verb
- Organize Verb
- Organize around Verb
- Organized Adj Past Participle Verb
- Orgasm Noun Verb Adj
- Orient Noun Verb Adj Pnoun
- Orientalise Verb
- Orientalize Verb
- Orientate Verb Past Participle Pres. Participle
- Orientated Adj Past Participle Verb
- Orienteer Noun Verb
- Originate Verb
- Originate in Verb
- Ornament Noun Verb Adj
- Ornate Adj Verb
- Orphan Noun Verb Adj Past Participle
- Orphrey Noun Verb Adj
- Orthogonalize Verb
- Orthonormalize Verb
- Orthophotograph Noun Adj Verb
- Oscillate Verb
- Osculate Verb
- Osmose Verb Noun
- Ossify Verb
- Ostler Noun Verb
- Ostracise Verb
- Ostracize Verb Past Participle
- Otter Noun Adj Verb
- Oubliette Noun Verb
- Ought Verb
- Ought not Verb
- Oughter Verb
- Oust Verb
- Out Adj Adv Prep Verb Noun
- Outargue Verb
- Outbalance Verb Noun Pres. Participle Past Participle