Countable Nouns That Start with O and End with ON

Explore 187 verified English countable nouns starting with O and ending with ON, including Organization, Operation, Opinion, Option, Occasion, Opposition and Observation. Sort these count nouns with singular and plural forms by word length for ESL grammar practice, determiner usage, and plural spelling below, or review singular and plural count rules in our noun grammar guide.

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Starts with OB24 words
observation
obligation
objection
obsession
obstruction
objectification
obliteration
obfuscation
oblation
obscuration
obtrusion
obviation
obstipation
obversion
objectivation
obturation
objectivization
objurgation
obduction
obtestation
obsoletion
obliquation
obsecration
obduration
Starts with OC13 words
occasion
occupation
octagon
occlusion
octahedron
occultation
octillion
octoroon
occidentalization
octodecillion
ocellation
octakishexahedron
octastichon
Starts with OD
1 words
odeon
Starts with OE
1 words
oerlikon
Starts with OF
2 words
offseason
officiation
Starts with OL
2 words
oligomerization
olecranon
Starts with OM4 words
omission
omicron
ombudsperson
omophorion
Starts with ON
2 words
onion
onomasticon
Starts with OO
1 words
oophoron
Starts with OP15 words
operation
opinion
option
opposition
optimization
oppression
operon
opsonization
opacification
ophiopogon
oppilation
opsonification
ophthalmencephalon
oppignoration
oppigneration
Starts with OR16 words
organization
orientation
orchestration
ordination
ornamentation
origination
oration
orison
orthogonalization
orientalization
orchestrion
orthicon
orillon
orpharion
orarion
orthopteron
Starts with OS6 words
oscillation
ostentation
ossification
osculation
ostracon
oscitation
Starts with OU
2 words
outstation
outmigration
Starts with OV24 words
ovulation
ovation
overreaction
overcorrection
oversimplification
overproduction
overrepresentation
overcompensation
overexertion
overconcentration
overestimation
overcomplication
overgeneralization
overvaluation
overextension
overexploitation
overregulation
overspecialization
overexpansion
overmedication
overdetermination
oversubscription
oviposition
overutilization
Starts with OX4 words
oxidation
oxymoron
oxidization
oxyanion
Starts with OZ
2 words
ozonation
ozonization

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