- Oxford blue
- outpost
- on every side of
- other side of the coin
- overzealous
- Old Nick
- overtire
- okey-dokey
- obtrusion
- oatmeal
- one after another
- open to change
- observed
- onrush
- old boy
- on the right track
- over-appreciative
- one hundred percent
- off the latch
- over the odds
- one's cards
- orison
- of the utmost importance
- out of harmony
- of yore
- overnighter
- on the wagon
- on the lookout
- overburden
- outback
- obscenities
- one-eighty
- opencast mine
- oriel
- one after the other
- on the same wave-length
- overvalue
- old lady
- omitted
- of unsound mind
- open to doubt
- one-party
- on the never-never
- occultation
- of the old school
- old-world
- occupier
- only to be expected
- of the order of
- on a level with
- offal
- on everyone's lips
- oceanic
- of value
- on the right lines
- on the attack
- open one's mouth
- ovid
- outpace
- occupied with
- oral tradition
- odysseys
- old saw
- on record
- outst-anding
- outer edge
- otherworldly
- outstanding payment
- overtired
- on offer
- overdraw
- orbshaped
- overplay
- one of a kind
- on one' own
- old codger
- ornithologist
- out of line
- opening statement
- on the assumption that
- of the wall
- old-maidish
- oppugnant
- on the bias
- of no value
- over-wrouht
- one's advancing years
- on the map
- on the strength of
- off the top of one's head
- obsolescence
- orient oneself
- oddment
- objectives
- on the quiet
- once and for all
- out of touch with reality
- only now
- one's career
- out of shape