- outlawry
- octennial
- outward seeming
- on the whole, all in all
- otherwise engaged
- over the top immoderate
- on the sly secretly
- oppugnancy
- on the shelf
- on the run at
- on the rocks
- out for the count
- on purpose
- on one's own solitary
- owing
- outstrip
- on the horns of a dilemma
- outrun
- other
- orgiastic
- on the dot
- organize
- oracular
- opt
- oppose
- one
- offset
- occupy
- of the essence
- obloquy
- on the level
- opening door
- on the house
- out of fashion
- oleograph
- out of range
- one above
- offshore
- one practised in adulation
- one who kisses
- over task
- obfuscate
- out-of-tune sound
- out roar
- objective
- out of the question
- obliging
- obliterate
- out of the ordinary
- oenophile
- ours
- otorhinolaryngology
- ostrich
- ostentatious
- ostenation
- off the point
- offence
- offer
- office
- officer
- overwrought
- overwhelm
- ossify
- old head on young shoulders
- old school
- origin
- old-time
- origami
- overthrow
- on firm or solid ground
- organized
- organ of sense
- orexis
- ore
- on the turn
- on the understanding
- optimism
- oppressive
- oncoming
- onerous
- opposite shore
- one hundred thousand
- one man rule
- one who has taken an additional wife
- one who lives by his writing
- open market
- opportunity
- open relationship
- open-mouthed
- overcrowded
- open-minded
- overconfident
- opprobrium
- oppugnent
- opt out
- optant
- optic axis
- optic nerve
- optimum
- ordinary green colouring