- oaf
- oafish
- Oahu
- Oahu Island
- oak
- oak apple
- oak blight
- oak chestnut
- oak fern
- Oak Leaf Cluster
- oak tree
- oak-leaved goosefoot
- oaken
- Oakland
- oakleaf goosefoot
- Oakley
- oakum
- oar
- oarfish
- oarlock
- oarsman
- oarsmanship
- oarswoman
- OAS
- oasis
- oast
- oast house
- oat
- oat cell carcinoma
- oatcake
- oaten
- Oates
- oath
- oatmeal
- oatmeal cookie
- Oaxaca
- Oaxaca de Juarez