- oleograph
- opposite bank
- old age home
- obtuse
- off one's onion
- oblivion
- overlie
- occlude
- off the hook
- on the horizon
- overstock
- occupational
- out of range
- over hastiness
- our lady
- offend
- open mind
- outsourcing
- of the first magnitude
- op
- oil tanker
- on parole
- orkut
- omninescience
- oste
- overexertion
- one above
- ointment
- old harry
- obscuration
- outdate
- once
- of a low standard
- on its last legs
- octet rule
- ooze
- osculatory
- obviously
- oxails
- opposition
- operose
- ornithology
- of mark
- object oriented programming
- offshore
- object computer
- oenology
- orator
- oblation
- odd
- ochre
- observance
- observant
- obsess
- obstreperous
- overboard
- occupation
- odds
- offender
- odds and ends
- offering
- off-key
- out bargain
- on
- one-time
- open air
- osteal
- operation
- opinion
- opposed
- open field
- opus
- ordain
- order someone
- ordinance
- organism
- orientation
- ostensibly
- ostracism
- ounce
- obesiance
- outlast
- outlet
- overact
- outright
- obfuscate
- over and above
- overdo
- outside verandha
- overcritical
- objective
- overly
- overriding
- overtone
- overwork
- overhang
- own up
- obliging
- on paper
- optative