- one's Ps and Qs
- on the lookout for
- orbicular
- ode
- on that occasion
- oncosts
- open-endedness
- or fashion
- of immeasurable value
- occurring in turns
- of no matter
- on the shore
- oubliette
- occurring each day
- open-handedness
- on the bush telegraph
- one day
- outpatient
- old dear
- on the straight and narrow
- outer layer
- ornithology covert
- onions
- outvote
- once more
- ornamented
- over-refined
- observation of
- owing someone a debt of gratitude
- on the verge of tears
- of no moment
- officers of the law
- over-appreciative
- outstretch
- opponents
- overlord
- on dry land
- ordered
- on every side of
- outturn
- on the slate
- on numerous occasions
- off-course
- obiter dictum
- opposers
- on the block
- obtrude on
- obligated to
- out of harm's way
- open-work
- open for discussion
- off the latch
- oiled
- of assistance
- of a kind
- over-sensational
- one's lot in life
- ocean-going
- overcurious
- ordination
- of the cuff
- overspend
- obliviousness
- overarching
- outmost
- or rather
- oviform
- on level with
- Ozalid
- outfits
- occupy oneself
- overwrite
- of immeasurable worth
- on your way
- old boy
- overfull
- onrush
- others
- observed
- obstacles
- on top of that
- over-elaborateness
- outcrop
- of age
- open to change
- one after another
- operating costs
- outflux
- on the jungle telegraph
- Oxford blue
- one-sidedness
- owing to the fact that
- old fashioned
- on vacation
- of little importance
- off the subject
- okey-dokey
- owing a debt of gratitude
- oatmeal
- on bended knee