- rhythm
- c.1557, from L. rhythmus "movement in time," from Gk. rhythmos "measured flow or movement, rhythm," related to rhein "to flow," from PIE base *sreu- "to flow" (see rheum). In M.L., rithmus was used for accentual, as opposed to quantitative, verse, and accentual verse was usually rhymed. Rhythm method of birth control attested from 1940. Rhythm and blues, U.S. music style, is from 1949.