hemicycle vs semicircle

hemicycle and semicircle both are nouns.

Word	Noun	Adjective	Verb	Adverb
hemicycle	Yes	No	No	No
semicircle	Yes	No	No	No

As nouns, hemicycle and semicircle are synonyms defined as:

hemicycle and semicircle: a plane figure with the shape of half a circle

hemicycle (noun)	semicircle (noun)
a plane figure with the shape of half a circle	a plane figure with the shape of half a circle