unholy (adj.)

Old English unhalig, "impious, profane, wicked," from un- (1) "not" + halig (see holy). Similar formation in Middle Dutch onheilich, Old Norse uheilagr, Danish unhellig, Swedish ohelig. In reference to actions, it is attested from late 14c. Colloquial sense of "awful, dreadful" is recorded from 1842.