dap · noun, verb1
Onomatopoeic, from the sound made when a person runs while wearing daps.
dap · noun, verb2
US 1971, originally by black soldiers during the Vietnam war, associated with Black Power movement. Originally an elaborate handshake, later specifically a fistbump. Verb originally give dap. Presumably onomatopoeic, or influenced by tap, dab, etc. Alternatively, from earlier slang usage as abbreviation of dapper. Also explained as an acronym, such as “Dignity for Afro People” or “Dignity And Pride”; this may be a backronym or unrelated, but accords with phrasal use as “give DAP” (compare “give respect”). More speculative etymologies derive it from Vietnamese đẹp (“beautiful”), though this is unlikely.
Etymology from Wiktionary, CC BY-SA 4.0.