mid-13c., "sacrifice by fire, burnt offering," from Old French holocauste (12c.), or directly from Late Latin holocaustum, from Greek holokauston "a thing wholly burnt," neuter of holokaustos "burned whole," from holos "whole" (from PIE root *sol- "whole, well-kept") + kaustos, verbal adjective of kaiein "to burn" (see caustic).
Originally a Bible word for "burnt offerings," given wider figurative sense of "massacre, destruction of a large number of persons" from 1670s. The Holocaust "Nazi genocide of European Jews in World War II," first recorded 1957, earlier known in Hebrew as Shoah "catastrophe." The word itself was used in English in reference to Hitler's Jewish policies from 1942, but not as a proper name for them.