word-forming element meaning "many, much, multi-, one or more," from Greek polys "much" (plural polloi), from PIE root *pele- (1) "to fill," with derivatives referring to multitudinousness or abundance. Equivalent to Latin multi-, it is properly used in compounds only with words of Greek origin. In chemical names, usually indicating a compound with a large number of atoms or molecules of the same kind (such as polymer).
c. 1600, "pertaining to rhythm in art," from French rhythmique or directly from Latin rhythmicus, from Greek rhythmikos, from rhythmos "measured flow or movement, rhythm; proportion, symmetry" (see rhythm). By 1630s of language, verse, music, etc., "marked by regularly recurring accents or beats," especially if strong or smooth. Related: Rhythmical (1560s); rhythmically.