fist-bump greeting, in African-American popular culture by 1972, with various theories as to origin and name meaning. Probably imitative (dap was used in 19c. for the bounce of a ball or the skip of a stone on water). Dap, meanwhile, is listed in the DAS as African-American vernacular c. 1950 for "aware, up to date," also "stylish, well-dressed," in the latter case at least a shortening of dapper. Controversial during the Vietnam War when used by U.S. soldiers, as it often was regarded by whites as a ritual act of black solidarity.