early 15c., dissonaunt, "at variance, disagreeing," from Old French dissonant (13c.) and directly from Latin dissonantem (nominative dissonans), present participle of dissonare "differ in sound," from dis- "apart" (see dis-) + sonare "to sound, make a noise" (from PIE root *swen- "to sound"). The meaning "discordant in sound, harsh" is from 1570s. Related: Dissonantly.
early 13c., sounen "to be audible, produce vibrations affecting the ear," from Old French soner (Modern French sonner) and directly from Latin sonare "to sound, make a noise" (from PIE root *swen- "to sound"). From late 14c. as "cause something (an instrument, etc.) to produce sound." Related: Sounded; sounding.
"unsubstantiated report, gossip, hearsay;" also "tidings, news, a current report with or without foundation," late 14c., from Old French rumor "commotion, widespread noise or report" (Modern French rumeur), from Latin rumorem (nominative rumor) "noise, clamor; common talk, hearsay, popular opinion," which is related to ravus "hoarse" (from PIE *reu- "to bellow").
Dutch rumoer, German Rumor are from French. The sense of "loud protest, clamor, outcry" also was borrowed in Middle English but is now archaic or poetic. Also compare rumorous "making a loud, confused sound" (1540s). Rumor-monger is by 1884 (earlier in that sense was rumorer, c. 1600). The figurative rumor mill is by 1887.
1530s (transitive), "to reject with scorn," from Latin explodere "drive out or off by clapping, hiss off, hoot off," originally theatrical, "to drive an actor off the stage by making noise," hence "drive out, reject, destroy the repute of" (a sense surviving in an exploded theory), from ex "out" (see ex-) + plaudere "to clap the hands, applaud," which is of uncertain origin. Athenian audiences were highly demonstrative. clapping and shouting approval, stamping, hissing, and hooting for disapproval. The Romans seem to have done likewise.
At the close of the performance of a comedy in the Roman theatre one of the actors dismissed the audience, with a request for their approbation, the expression being usually plaudite, vos plaudite, or vos valete et plaudite. [William Smith, "A First Latin Reading Book," 1890]
English used it to mean "drive out with violence and sudden noise" (1650s), later "cause to burst suddenly and noisily" (1794). Intransitive sense of "go off with a loud noise" is from 1790, American English; figurative sense of "to burst with destructive force" is by 1882; that of "burst into sudden activity" is from 1817; of population by 1959. Related: Exploded; exploding.