before vowels often is-, word-forming element meaning "equal, similar, identical; isometric," from Greek isos "equal to, the same as; equally divided; fair, impartial (of persons); even, level (of ground)," as in isometor "like one's mother." In English used properly only with words of Greek origin; the Latin equivalent is equi- (see equi-).
word-forming element meaning "generating, producing, yielding;" see -gen + -ous. In modern formations, making adjectives corresponding to words in -gen. In some older words, from Late Latin -genus, from Latin -gena "born" (for example indigenous).