- rhythm (n.)
- 1550s, from Latin rhythmus "movement in time," from Greek rhythmos "measured flow or movement, rhythm," related to rhein "to flow," from PIE root *sreu- "to flow" (see rheum). In Medieval Latin, rithmus was used for accentual, as opposed to quantitative, verse, and accentual verse was usually rhymed. Rhythm method of birth control attested from 1936. Rhythm and blues, U.S. music style, is from 1949 (first in "Billboard").