O

oath

obey

object

obligation

oblige

obscure

observe

obsolete

obstacle

obstinate

obstruct

obtain

occasion

occasionally

occupy

occur

odd

odor

offend

offer

official

offspring

omit

oppose

oppress

optimism

oral

orbit

ordeal

order

ordinary

organize

origin

originate

ornament

orphan

outcome

outfit

outlet

outlook

outrage

outstanding

overcome

overlook

overtake

overwhelming

owe

own

owner

oxygen