- one who has attained majority
- one who ploughs
- once for all
- out dare
- oath taking
- oniony
- obscene language
- ontological
- old wine in a new bottle
- oculus
- of many forms
- owlet
- old before one time
- operant
- oppressing others
- oviducal
- owl
- one who earns
- oneirology
- ootheca
- occuring daily
- opposite side
- oscitant
- on request
- omni volume
- optative
- ovine
- original sin
- octopede
- off one's hand
- override, overrule
- of old standing
- on the round
- out-tray
- out and about
- over haste
- outstay
- oligarch
- oarswoman
- obdurate
- obedient
- obese
- obscure
- observer
- obsidian
- obstacle
- obstinacy
- obstinate
- obstinate man
- obviate
- odour
- odyssey
- of necessity
- off-day
- off-putting
- offby heart
- offerings of flowers
- office hunter
- official
- offing in
- ogle
- oh
- oil-bath
- oil-vessel
- ok
- old
- omanization
- omission
- omnipotent
- omniscient
- omr
- on the files
- one place
- one roaming
- one which deserves to be imitated
- one who creates
- one who enjoys
- one who shaves
- one-act play
- one-man show
- open heart
- open letter
- open question
- open the floodgates
- open-handed
- opposing
- oppressed
- optic circle
- optical instrument
- optimalise
- organic farming
- organically
- organising
- organist
- orgy
- orifice
- original tissue
- ossification
- osteopath
- other-worldly