- outrun
- open-air theatre
- outstrip
- outwit
- occiput
- owing
- on one's own solitary
- ovicular
- obsequiousness
- overstay
- ozoneferous
- on purpose
- oak
- on the rocks
- oldish
- on the run at
- onion
- on the shelf
- ones soul for
- on the sly secretly
- outnumber
- obsolete
- overabundant
- obstetric
- on all fours
- on the surface
- overprint
- obstetrician
- over the top immoderate
- oxter
- otherwise engaged
- oil lamp
- obstruct
- on the whole, all in all
- oversell
- out of one's own head
- omni competent
- on one's heels
- on an even keel
- one who punishes
- outward seeming
- only resort
- ordurous
- oil resource
- of one's own making
- obtain
- obtainable
- obtuse angle
- obviousness
- occasion
- of one's own accord
- of one's own free will
- overlook
- overlay
- overjoyed
- overcrowded
- offload
- offone'sguard
- offshoot
- ogre
- oikos
- oil pot
- oil-cloth
- oil-engine
- oilman
- oily
- overconfident
- omit
- overbearing
- omnifarous
- omnipresent
- omnivorous
- over worn
- over sleepy
- on the rack
- outshine
- output
- one man rule
- outnumbered
- one who has taken an additional wife
- one who lives by his writing
- only-begotten
- outmanoeuvre
- onus probandi
- ownership
- opprobrium
- oppugnent
- opt out
- optant
- optic axis
- optic nerve
- optimum
- ordinary green colouring
- ordure
- organic analysis
- organic disease
- organza
- orient, orientate
- orientalist
- ostler