Countable Nouns That Start with O
Browse 1,840 English countable nouns starting with the letter O, including Open, Order, Office, Okay, Organization, Offer and Operation. Sort these count nouns with singular and plural forms by letter count for ESL grammar practice, determiner usage, and plural spelling, or consult our noun grammar guide.
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Starts with OA19 words
oath
oasis
oatmeal
oar
oat
oaf
oakwood
oarsman
oast
oater
oarlock
oatcake
oarfish
oakleaf
oarswoman
oasthouse
oakling
oarweed
oanshagh
Starts with OB24 words
object
objective
observation
obligation
obstacle
objection
observer
obsession
obedience
obstruction
obsessive
obscurity
observable
obituary
oblique
observance
observatory
obscenity
obsidian
oboe
objector
oblong
objectification
obliteration
Starts with OC24 words
ocean
occasion
occupation
occurrence
occupancy
occupant
octopus
octave
octagon
ocular
octane
oceanfront
oceanside
occupier
octet
octogenarian
ocelot
occlusion
occultist
oculus
oceanview
occidental
ocarina
ocher
Starts with OD24 words
odd
odor
odyssey
ode
oddity
oddball
oddness
odeon
oddsmaker
oddment
odorant
odalisque
odeum
oda
odontoid
odawa
odal
odist
odontoblast
odonate
odontocete
odontoma
odontologist
odontalgia
Starts with OE13 words
oeuvre
oenophile
oersted
oerlikon
oe
oenologist
oedometer
oenothera
oeillade
oenophilist
oenomel
oecist
oenometer
Starts with OF24 words
off
office
offer
official
officer
offense
offensive
offering
offset
offender
offspring
offseason
offside
officeholder
offload
offshoot
offbeat
officiant
offramp
offertory
offeror
offtake
officemate
offeree
Starts with OG11 words
ogre
ogle
ogee
ogive
ogress
ogham
ogler
ogdoad
ogonek
ogrefish
oghamist
Starts with OH5 words
oh
ohm
ohmmeter
ohia
ohmage
Starts with OI24 words
oil
ointment
oi
oiler
oilfield
oink
oilcloth
oilman
oilseed
oilcan
oilskin
oik
oilpan
oilstone
oilpaper
oidium
oilbird
oilfish
oilway
oikist
oilhole
oilery
oilcup
oilnut
Starts with OJ
1 words ojime
Starts with OK11 words
ok
okay
okra
okie
okapi
oke
okanogan
okeydoke
oka
okta
okimono
Starts with OL24 words
olympics
oliver
olive
oligarchy
oldie
oligarch
olfactory
ollie
oleander
oligopoly
oligo
oldster
oleo
olympiad
oligonucleotide
oligomer
olefin
olivine
oliphant
ology
olio
olla
oligosaccharide
oligodendrocyte
Starts with OM24 words
omission
omen
omega
ombudsman
om
omicron
omelet
omnibus
omnipotent
omnivore
omniscient
omani
ombre
omeprazole
ombudsperson
omakase
oma
omnium
omentum
ombuds
omer
omnisexual
omnishambles
omphalos
Starts with ON24 words
one
onion
ongoing
onset
onboarding
ontology
onslaught
onlooker
oncoming
onus
oncologist
onesie
onyx
onomatopoeia
onside
oncogene
onrush
ono
onigiri
onliner
ontogeny
oncovirus
ontologist
oncer
Starts with OO24 words
ooh
oops
ooze
oof
oolong
oop
oodles
oo
oocyte
oompah
oom
oom-pah-pah
oocyst
oogonium
oolite
oophorectomy
ootheca
oologist
oont
oosphere
oospore
oojamaflip
oophorosalpingectomy
ootid
Starts with OP24 words
open
operation
opportunity
opinion
option
opening
opposite
opposition
opponent
operator
opera
optional
optimization
oppression
opioid
optics
opaque
op
optimum
opener
operative
opacity
optimist
opiate
Starts with OQ
1 words oquassa
Starts with OR24 words
order
organization
original
organic
ordinary
origin
orange
organ
orientation
oral
organism
organizer
orbit
orchestra
orderly
ore
orthodox
originality
orchard
oracle
orphan
orb
orgasm
ornament
Starts with OS24 words
oscars
ostrich
osmosis
oscillation
oscillator
osprey
ostracism
os
ostentation
ostomy
oscilloscope
osteopathy
osteopath
ossification
ostler
osmolarity
osteosarcoma
osteoid
osteria
ostia
ossuary
osteonecrosis
osteocyte
osteomyelitis
Starts with OT24 words
other
ottoman
otter
otto
othering
otaku
otherworld
otoscope
ottawan
oto
otolith
otorhinolaryngologist
otoplasty
otologist
otoscopy
ottavino
otalgia
ottava
otocinclus
otarine
otterhound
otosclerotic
otary
otiosity
Starts with OU24 words
out
outside
ought
outcome
output
outer
outline
outfit
outlet
outlook
outrage
ounce
outsider
outreach
outbreak
outward
outgoing
ouch
outlaw
outage
outing
outskirts
outset
outcast
Starts with OV24 words
over
overall
overnight
overview
overlook
overhead
oversight
overtime
overdose
override
oval
overlap
overflow
overthrow
overturn
overload
overlay
ovary
overhaul
overture
overrun
overalls
overhang
overseer
Starts with OW12 words
owner
ownership
owl
owens
owo
owie
owlet
owlery
ower
owler
owelty
owerloup
Starts with OX24 words
oxford
ox
oxide
oxidation
oxymoron
oxycodone
oxy
oximeter
oxtail
oxidant
oxidizer
oxidase
oxalate
oxidization
oxbow
oxblood
oxazepam
oxcart
oxygenator
oxalis
oxo
oxheart
oxtongue
oxaloacetate
Starts with OY7 words
oyster
oy
oyez
oystercatcher
oyer
oysterman
oysterer
Starts with OZ12 words
ozark
ozeki
ozonation
ozarkian
ozonolysis
ozonization
ozonide
ozalid
ozonizer
ozonosphere
ozothamnus
ozokerite