Countable Nouns That Start with O and End with SIS

Explore 17 verified English countable nouns starting with O and ending with SIS, including Oasis, Osmosis, Overemphasis, Overdiagnosis, Overanalysis, Osteonecrosis and Organogenesis. 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 ON
2 words
onomatopoiesis
onychocryptosis
Starts with OP
2 words
ophthalmomycosis
ophthalmodiagnosis
Starts with OR3 words
organogenesis
orthosis
orogenesis
Starts with OS5 words
osmosis
osteonecrosis
osteoarthrosis
osteopetrosis
osteoclasis
Starts with OV3 words
overemphasis
overdiagnosis
overanalysis
Starts with OZ
1 words
ozonolysis

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