Old English dom "law, judgment, condemnation," from Proto-Germanic *domaz (cf. Old Saxon and Old Frisian dom, Old Norse domr, Old High German tuom, Gothic doms "judgment, decree"), from PIE root *dhe- (cf. Sanskrit dhaman- "law," Greek themis "law," Lithuanian dome "attention"), literally "to set, put" (see factitious). A book of laws in Old English was a dombec. Modern sense of "fate, ruin, destruction" is c.1600, from the finality of the Christian Judgment Day.
late 14c., from doom (n.). Related: Doomed; dooming.