- One-of-a-kind Adj Noun
- One-off Adj Noun Adv
- One-on-one Adj Adv Noun
- One-partner Adj
- One-seater Noun Adj
- One-seeded Adj Past Participle
- One-sided Adj
- One-size Adj
- One-third Adj Noun Num
- One-time Adj
- One-to-one Adj Adv Noun
- One-up Verb Adj Noun
- One-way Adj Noun Adv
- One-year Adj
- Onearmed Adj
- Onedimensional Adj
- Oneeyed Adj
- Onefold Adj Adv
- Oneiric Adj
- Oneirocatatonic Adj
- Oneirocritic Adj Noun
- Oneirocritical Adj
- Oneiroid Adj
- Oneirophrenia Noun Adj
- Onely Adj Adv
- Oneness Noun Adj
- Onerous Adj
- Onesided Adj
- Onesie Noun Adj
- Onetime Adj Noun
- Ongoing Adj
- Onion Noun Adj
- Onion-like Adj
- Onionskin Noun Adj
- Oniony Adj
- Oniony-tasting Adj
- Oniric Adj
- Onlay Noun Adj
- Online Adj Adv
- Onlooker Noun Adj
- Onlooking Noun Adj
- Only Adj Adv Conj
- Onomastic Adj
- Onomatopoeic Adj
- Onomatopoeical Adj
- Onomatopoetic Adj
- Onrushing Adj Pres. Participle
- Onscreen Adj Adv
- Onset Noun Adj
- Onshore Adj Adv
- Onsite Adj Adv
- Onstage Adj Adv
- Onstream Adj Adv
- Ontario Noun Pnoun Adj
- Ontogenetic Adj
- Ontogenetical Adj
- Ontogenic Adj
- Ontogenical Adj
- Ontologic Adj
- Ontological Adj