ocean vs. sea
offender vs. wrongdoer
observer vs. percipient
outlaw vs. unlawful
ostiary vs. porter
officeholder vs. officer
officer vs. policeman
overseer vs. superintendent
oldtimer vs. warhorse
owner vs. proprietor
owner vs. possessor
oculist vs. ophthalmologist
oculist vs. optometrist
orator vs. speechmaker
orator vs. rhetorician
orator vs. speechifier
orderer vs. systematizer
orderer vs. systematiser
orderer vs. systemizer
orderer vs. systemiser
orderer vs. systematist
oarsman vs. rower
occupier vs. resident
offerer vs. offeror
orthopaedist vs. orthopedist
osteologer vs. osteologist
osteopath vs. osteopathist
occupant vs. resident
overcomer vs. subduer
overextend vs. overstrain
orach vs. orache
oxlip vs. paigle
obeche vs. samba
obechi vs. samba
orris vs. orrisroot
oxalis vs. sorrel
oca vs. oka
outgo vs. surpass
outgo vs. outstrip
outgo vs. outmatch
outdo vs. outgo
outgo vs. surmount
outgo vs. outperform
overcharge vs. pluck
opsonisation vs. opsonization
oxidation vs. oxidization
oxidation vs. oxidisation
omnipresence vs. ubiquity
oestrus vs. rut
ornithosis vs. psittacosis
ophthalmia vs. ophthalmitis
oscheocele vs. oscheocoele
odontalgia vs. toothache
ozaena vs. ozena
oreide vs. oroide
oxidant vs. oxidizer
oxidant vs. oxidiser
ordure vs. stool
olibanum vs. thus
oligoclase vs. plagioclase
oxalacetate vs. oxaloacetate
ola vs. olla
orthophosphate vs. phosphate
oxyhaemoglobin vs. oxyhemoglobin
olein vs. triolein
overclothe vs. overdress
overtire vs. overweary
overfatigue vs. overtire
overstretch vs. pull
operate vs. recrudesce
operate vs. run
oxygenate vs. oxygenise
oxygenate vs. oxygenize
ossify vs. petrify
oxidate vs. oxidize
oxidate vs. oxidise
occur vs. pass
organize vs. unionise
organize vs. unionize
organise vs. unionise
organise vs. unionize
occidentalize vs. westernize
occidentalize vs. westernise
occidentalise vs. westernize
occidentalise vs. westernise
occupy vs. take
occupy vs. reside
overleap vs. vault
opt vs. prefer
opine vs. think
observe vs. watch
observe vs. respect
overpower vs. overwhelm
overmaster vs. overwhelm
overwhelm vs. submerge
overcome vs. overwhelm
overtake vs. overwhelm
overwhelm vs. whelm
oppose vs. pit
oppose vs. react
objurgate vs. reprobate
overemphasize vs. overstress
overemphasise vs. overstress
oppugn vs. question
outpoint vs. outscore
outmaneuver vs. outsmart
outmanoeuvre vs. outsmart
outrival vs. outvie
overtake vs. pass
outweigh vs. overbalance
outweigh vs. preponderate
outbalance vs. outweigh
offsaddle vs. unsaddle
offload vs. unload
overproduce vs. overproduce
originate vs. start
originate vs. rise
overcrop vs. overcultivate
offend vs. pique
outride vs. stay
oscillate vs. vibrate
odorize vs. scent
odorise vs. scent
odourise vs. scent
overstep vs. trespass
overstep vs. pass
ostentate vs. swank
overshadow vs. shadow
oppress vs. persecute
outlive vs. survive
outlast vs. survive
overwinter vs. winter
outrank vs. rank
overspread vs. spread
plum vs. plumb
plumb vs. right
plumb vs. sublimely
plumb vs. stark
plumb vs. plummet
pat vs. slick
pat vs. tap
partially vs. partly
part vs. partially
part vs. portion
part vs. parting
part vs. role
part vs. voice
part vs. region
part vs. piece
part vs. share
part vs. separate
part vs. start
plainly vs. simply
poorly vs. sickly
presently vs. soon
passionately vs. stormily
plain vs. spare
plain vs. unembellished
plain vs. unornamented
plain vs. unvarnished
plain vs. unmistakable
patent vs. plain
plain vs. unpatterned
plain vs. sheer
plain vs. unmixed
plain vs. unmingled
plain vs. purl
particularly vs. peculiarly
peculiarly vs. specially
potent vs. powerful
passing vs. super
passing vs. screamingly
passing vs. transient
passing vs. transitory
pass vs. passing
passage vs. passing
presumably vs. presumptively
piercingly vs. shrilly
painfully vs. sorely
preferably vs. sooner
preferably vs. rather
promptly vs. readily
promptly vs. pronto
promptly vs. quickly
plausibly vs. probably
purportedly vs. supposedly
predominantly vs. preponderantly
publically vs. publicly
plentifulness vs. plenty
plenteousness vs. plenty
plenitude vs. plenty
plentitude vs. plenty
plenty vs. sight
purely vs. strictly
periodically vs. sporadically
productively vs. profitably
properly vs. right
pleasantly vs. sunnily