Old English hefig "heavy, having much weight; important, grave; oppressive; slow, dull," from Proto-Germanic *hafiga "containing something; having weight" (cf. Old Saxon, Old High German hebig, Old Norse hofugr, Middle Dutch hevich, Dutch hevig), from PIE *kap- "to grasp" (see capable). Jazz slang sense of "profound, serious" is from 1937 but would have been comprehensible to an Anglo-Saxon. Heavy industry recorded from 1932. Heavy metal attested by 1839 in chemistry; in nautical jargon from at least 1744 in sense "large-caliber guns on a ship.
As a type of rock music, from 1972.