Countable Nouns That Start with O and End with IS

Explore 33 verified English countable nouns starting with O and ending with IS, including Oasis, Osmosis, Overemphasis, Overdiagnosis, Overanalysis, Osteonecrosis and Osteomyelitis. 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 OA
1 words
oasis
Starts with OC
1 words
occipitofrontalis
Starts with OL
1 words
olecranarthritis
Starts with ON3 words
onomatopoiesis
onychocryptosis
onychitis
Starts with OP5 words
ophthalmomycosis
ophthalmodiagnosis
ophthalmomyositis
ophthalmoneuritis
ophthalmorrhexis
Starts with OR10 words
organogenesis
orris
orbicularis
orchis
orthosis
orogenesis
ornis
orexis
orchiepididymitis
orthoaxis
Starts with OS6 words
osmosis
osteonecrosis
osteomyelitis
osteoarthrosis
osteopetrosis
osteoclasis
Starts with OV4 words
overemphasis
overdiagnosis
overanalysis
ovotestis
Starts with OX
1 words
oxalis
Starts with OZ
1 words
ozonolysis

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