alienation (n.)

late 14c., "transfer of ownership, action of estranging," from Old French alienacion and directly from Latin alienationem (nominative alienatio) "a transfer, surrender, separation," noun of action from past-participle stem of alienare "to make another's, part with; estrange, set at variance," from alienus "of or belonging to another person or place," from alius "another, other, different," from PIE root *al- (1) "beyond."

Middle English alienation also meant "deprivation of mental faculties, insanity" (early 15c.), from Latin alienare in a secondary sense "deprive of reason, drive mad;" 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.