- Optimistic Adj
- Optimistical Adj
- Optimized Adj
- Optimum Adj Noun
- Optional Adj
- Optoacoustic Adj
- Optoelectronic Adj
- Optogalvanic Adj
- Optokinetic Adj
- Optomechanical Adj
- Optometric Adj
- Optometrical Adj
- Opulent Adj
- Oracular Adj
- Oral Adj Noun
- Orange Adj Noun
- Orangeish Adj
- Orangey Adj
- Orangish Adj
- Orangy Adj
- Oratorial Adj
- Oratoric Adj
- Oratorical Adj
- Orbed Adj
- Orbicular Adj
- Orbicularis Adj Noun
- Orbiform Adj
- Orbital Adj Noun
- Orbiting Adj
- Orbitonasal Adj
- Orbitosphenoidal Adj
- Orbitotemporal Adj
- Orcadian Adj Noun
- Orchestic Adj
- Orchestral Adj
- Orchestrated Adj
- Orchidaceous Adj
- Orchidean Adj
- Orchilytic Adj
- Orchitic Adj
- Ordained Adj
- Orderable Adj
- Ordered Adj
- Orderless Adj
- Orderly Adj
- Ordinal Adj Noun
- Ordinary Adj Noun
- Ordinate Adj Noun Verb
- Ordovician Adj Noun
- Ordurous Adj
- Orectic Adj
- Oregenetic Adj
- Oregonian Adj Noun
- Oreless Adj
- Organic Adj
- Organical Adj
- Organicistic Adj
- Organisational Adj
- Organised Adj
- Organismal Adj