Countable Nouns That Start with O and End with O

Explore 31 verified English countable nouns that start and end with O, including Outro, Oregano, Otto, Ortho, Oppo, Oligo and Oratorio. 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.