oak

obedience

obedient

obey

object

objection

objective

obligation

oblige

obscure

obscurity

observation

observe

observer

obsession

obsolete

obstacle

obstruct

obstruction

obtain

obvious

occasion

occasional

occupant

occupation

occupational

occupy

occur

occurrence

ocean

October

odd

off

offend

offender

offense

offensive

offer

office

officer

official

offset

offspring

oil

old

omit

one

ongoing

onion

online

only

onward

open

opera

operate

operation

operational

operative

operator

opinion

opponent

opportunity

oppose

opposite

opposition

oppress

oppression

oppressive

optimistic

option

optional

oral

orange

orbit

orchestra

order

ordinary

organ

organic

organism

organization

organize

orient

origin

original

originate

other

ought

ounce

outbreak

outcome

outdoor

outer

outfit

outlet

outline

outlook

outnumber

output

outrage

outrageous

outset

outside

outsider

outstanding

outweigh

oven

overall

overcome

overdo

overdue

overestimate

overhead

overlap

overlook

overpower

oversee

oversight

overtake

overthrow

overtime

overturn

overweight

overwhelm

overwhelming

owe

own

owner

ownership

oxygen

ozone