early 14c., rappe, "a quick, light blow; a resounding stroke," also "a fart" (late 15c.), native or borrowed from a Scandinavian source (compare Danish rap, Swedish rapp "light blow"); either way probably of imitative origin (compare slap, clap).

Slang meaning "a rebuke, the blame, responsibility" is from 1777; specific meaning "criminal indictment" (as in rap sheet, 1960) is from 1903; to beat the rap is from 1927. Meaning "music with improvised words" was in New York City slang by 1979 (see rap (v.2)).

also slap-dash, 1670s, "in a hasty, abrupt manner, with or as with a slap and a dash," from slap (v.) + dash (v.). As an adjective, "dashing, offhand, careless," from 1792. As a noun, "rough-coat, coarse plaster," applied as a preservative to exterior walls, from 1796.

"large or impressive person or thing," attested by 1781 in glossaries of Northern dialect, agent noun from slap (v.). Compare whopper. By 1886 as "implement for slapping."

also slap-shot, in ice hockey, a shot made with a slapping motion of the stick, 1942, from slap (v.) + shot (n.).

also slap-stick, originally (1896) a device consisting of two sticks fastened together so as to slap loudly when a clown or actor hits somebody with it, or else used to make a sound-effect offstage; from slap and stick (n.).

As an adjective by 1906. The meaning "farcical physical comedy, horseplay" (1916) is short for slapstick comedy or humor.