O.E. unhalig, "impious, profane, wicked," from
un- (1) "not" + halig (see
holy). Cf. M.Du. onheilich, O.N. uheilagr, Dan. unhellig, Swed. ohelig. In ref. to actions, it is attested from 1382. Colloquial sense of "awful, dreadful" is recorded from 1842.