Proto-Indo-European root meaning "strong, great." It forms all or part of: ameliorate; amelioration; meliorate; melioration; meliorism; multi-; multiform; multiple; multiply; multitude. It is the hypothetical source of/evidence for its existence is provided by: Greek mala "very, very much;" Latin multus "much, many," melior "better."
"having or exhibiting many or various forms," 1785, from Greek polymorphos "multiform, of many forms, manifold," from polys "many" (from PIE root *pele- (1) "to fill") + morphē "shape, form," a word of uncertain etymology. Especially of insects: "undergoing a series of marked changes during development." Related: Polymorphic; polymorphously; polymorphousness.