"transfer of ownership," late 14c., from Old French alienacion and directly from Latin alienationem (nominative alienatio) "a transfer, surrender," noun of action from past participle stem of alienare (see alienate). It also meant "loss or derangement of mental faculties, insanity" (late 15c.), hence alienist. Phrase alienation of affection as a U.S. legal term in divorce cases for "falling in love with someone else" dates to 1861.