- oxytetracycline hydrochloride
- oxytocic
- oxytocic drug
- oxyura
- oxytropis lambertii
- oxytropis
- oxytocin
- oxyura jamaicensis
- oxyuranus
- oxyuranus scutellatus
- oxyuridae
- oyster
- oyster agaric
- oyster bank
- oyster bar
- oyster crab
- oyster bed
- oyster dressing
- oyster fish
- oyster mushroom
- oyster shell
- oyster stew
- oyster stuffing
- obverse
- obversion
- obvious
- occam
- occasion
- occidental
- occupancy
- occupational hazard
- occupies
- ocean sunfish
- oceanic bird
- oceanites
- oceanus
- ocellus
- ocha
- ocher
- oyster catcher
- oyster park
- ochotona
- ochre_coloured dress
- ochs
- ocimum basilicum
- ockham
- ochrous
- oclock
- oconee bells
- ocotillo