Countable Nouns That Start with O and End with ION

Explore 165 verified English countable nouns starting with O and ending with ION, 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 OC8 words
occasion
occupation
occlusion
occultation
octillion
occidentalization
octodecillion
ocellation
Starts with OF
1 words
officiation
Starts with OL
1 words
oligomerization
Starts with OM
2 words
omission
omophorion
Starts with ON
1 words
onion
Starts with OP12 words
operation
opinion
option
opposition
optimization
oppression
opsonization
opacification
oppilation
opsonification
oppignoration
oppigneration
Starts with OR12 words
organization
orientation
orchestration
ordination
ornamentation
origination
oration
orthogonalization
orientalization
orchestrion
orpharion
orarion
Starts with OS5 words
oscillation
ostentation
ossification
osculation
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 OX3 words
oxidation
oxidization
oxyanion
Starts with OZ
2 words
ozonation
ozonization

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