- on the lookout for
- one's Ps and Qs
- over-scrupulousness
- overhand
- occurring each day
- oubliette
- on the shore
- occurring in turns
- or fashion
- onions
- on the straight and narrow
- oblivious to
- ode
- orbicular
- old dear
- one of these days
- on the bush telegraph
- operating
- ovule
- of a mind
- open-ended
- outvote
- one day
- ornamented
- overtop
- open-handedness
- on a par
- on the slate
- on every side of
- of no moment
- opposers
- out of harm's way
- on an equal footing
- on the block
- obligated to
- obtrude on
- Ozalid
- of assistance
- overwrite
- outflux
- oviform
- outturn
- of age
- or rather
- observation of
- overlord
- occupy oneself
- open-work
- on the verge of tears
- open for discussion
- outmost
- overarching
- over-appreciative
- ordered
- obliviousness
- overspend
- outfits
- on numerous occasions
- of the cuff
- ordination
- overcurious
- one or two
- ocean-going
- over-sensational
- off-course
- of a kind
- oiled
- off the latch
- obiter dictum
- opponents
- on dry land
- on level with
- owing someone a debt of gratitude
- oatmeal
- overtire
- open to change
- officers of the law
- off drugs
- over the odds
- one hundred percent
- of immeasurable worth
- owing to the fact that
- one's marching orders
- outrageousness
- on vacation
- old fashioned
- off the subject
- Oxford blue
- on your way
- over-elaborateness
- observed
- of one voice
- other side of the coin
- okey-dokey
- on the jungle telegraph
- on the right track
- outpost
- onrush
- on top of that
- Old Nick