homo- (1)

before vowels hom-, word-forming element meaning "same, the same, equal, like" (opposed to hetero-), from Greek homos "one and the same," also "belonging to two or more jointly," from PIE *somo-, from root *sem- (1) "one; as one, together with."

word-forming element meaning "homosexual," abstracted since early 20c. from homosexual, and ultimately identical to homo- (1).