Is it ensure, insure, or assure?
c.1300, "a quick, light blow, stroke," also "a fart" (late 15c.), native or borrowed from a Scandinavian source (cf. Danish rap, Swedish rapp "light blow"); either way probably of imitative origin (cf. slap, clap).
Slang meaning "rebuke, blame, responsibility" is from 1777; specific meaning "criminal indictment" (cf. rap sheet, 1960) is from 1903. To beat the rap is from 1927. Meaning "music with improvised words" first in New York City slang, 1979 (see rap (v.2)).
mid-14c., "strike, smite, knock," from rap (n.). Related: Rapped; rapping. To rap (someone's) knuckles "give light punishment" is from 1749. Related: Rapped; rapping.
"talk informally, chat," 1929, popularized c.1965 in Black English, possibly first in Caribbean English and from British slang meaning "say, utter" (1879), originally "to utter a sudden oath" (1540s), ultimately from rap (n.). As a noun in this sense from 1898. Meaning "to perform rap music" is recorded by 1979. Related: Rapped; rapping.
A form of pop music characterized by spoken or chanted rhymed lyrics, with a syncopated, repetitive accompaniment. Rap music originated in the second half of the twentieth century in black urban communities. (See also hip-hop.)
[origin unknown; perhaps related to repartee, perhaps to rapport, perhaps to rapid]