Merriam-Webster's Collegiate Dictionary:
off-site
off-speed
off-the-books
off-the-cuff
off-the-peg
off-the-rack
off-the-record
off-the-shelf
off-the-wall
off-white
offal
offaly
offbeat
offcast
offcut
offenbach
offence
offend
offender
offense
offenseless
offensive
offensively
offensiveness
offer
offering
offertory
offhand
offhanded
offhandedly
offhandedness
office
office boy
officeholder
officer
officer of arms
official
officialdom
officialese
officialism
officially
officiant
officiary
officiate
officiation
officinal
officious
officiously
officiousness
offing
offish
offishness
offprint
offscouring
offscreen
offset
offshoot
offshore
offside
offspring
offstage
offtrack
oft
often
oftentimes
ofttimes
og
ogadai
ogaden
ogam
ogasawara islands
ogbomosho
ogdai
ogden
ogee
ogeechee
ogham
oghamic
oghamist
ogival
ogive
ogle
ogler
oglethorpe
ogre
ogreish
ogress
oh
oh?e
ohia
ohia lehua
ohio
ohioan
ohlin
ohm
ohm's law
ohmic
