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.