- occurring in turns
- on a par with
- one's Ps and Qs
- on the lookout for
- orbicular
- on that occasion
- ornamented
- or fashion
- outvote
- over-refined
- occurring each day
- on a par
- old chestnut
- open-handedness
- ornithology covert
- operating
- ossuary
- open-ended
- of a mind
- ovule
- one of these days
- of no matter
- of immeasurable value
- overhand
- old master
- or the like
- on the straight and narrow
- on an equal footing
- of no moment
- outfits
- outflux
- on the verge of tears
- owing someone a debt of gratitude
- opponents
- overlord
- occupy oneself
- of immeasurable worth
- overwrite
- of assistance
- one-sidedness
- on dry land
- ordered
- of age
- on every side of
- open-work
- open for discussion
- on numerous occasions
- off-course
- obiter dictum
- over-sensational
- ocean-going
- observation of
- outturn
- out of harm's way
- on the slate
- of a kind
- opposers
- Ozalid
- off the latch
- on the block
- oiled
- obtrude on
- overcurious
- ordination
- of the cuff
- overspend
- obliviousness
- overarching
- outmost
- or rather
- oviform
- obligated to
- on level with
- one or two
- over-appreciative
- outstretch
- of little importance
- overfull
- off the subject
- outreach
- on bended knee
- overtire
- Old Nick
- other side of the coin
- outpost
- old warhorse
- Oxford blue
- oatmeal
- on vacation
- outrageousness
- owing to the fact that
- on top of that
- of one voice
- one hundred percent
- old fashioned
- open to change
- others
- obtrusion
- okey-dokey
- overzealous