dap (n.)

fist-bump greeting, with various theories as to origin and name meaning. In African-American popular culture by 1972 and 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. 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.