oath (noun)
promise
object (noun)
aim
object (verb)
oppose, disagree
objection (noun)
disagreement
oblige (verb)
please
obstinate (adjective)
stubborn
occupy (verb)
fill
occur (verb)
happen
odour (noun)
smell
offend (verb)
insult
omen (noun)
sign
oppress (verb)
ill-treat, crush
option (noun)
choice
ordeal (noun)
difficulty, trial, torment
origin (noun)
beginning