late 15c., from French estrangier "to alienate," from Vulgar Latin *extraneare "to treat as a stranger," from Latin extraneus "foreign, from without" (see strange). Related: Estranged.
1510s, "transfer to the ownership of another;" 1540s, "make estranged" (in feelings or affections), from Latin alienatus, past participle 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." Related: Alienated; alienating.
In Middle English the verb was simply alien, from Old French aliener and directly from Latin alienare. It is attested from mid-14c. in theology, "estrange" (from God, etc.; in past participle aliened); late 14c. as "break away (from), desert;" c. 1400 in law, "transfer or surrender one's title to property or rights."
"one who scientifically treats or studies mental illness," 1864, from French aliéniste, from alienation in the sense of "insanity, loss of mental faculty," from Latin alienare "deprive of reason, drive mad," literally "to make another's, estrange" (see alienate). The mental sense of alienare has since mostly died out in English, but Middle English had aliened from mind "deranged, not rational" (late 14c.), and alienation was used from 15c. in a sense of "loss or derangement of mental faculties, insanity."
late 13c., straunge, "from elsewhere, foreign, unknown, unfamiliar, not belonging to the place where found," from Old French estrange "foreign, alien, unusual, unfamiliar, curious; distant; inhospitable; estranged, separated" (Anglo-French estraunge, strange, straunge; Modern French étrange), from Latin extraneus "foreign, external, from without" (source also of Italian strano "strange, foreign," Spanish extraño), from extra "outside of" (see extra-). In early use also strounge. The surname Lestrange is attested from late 12c. Sense of "queer, surprising" is attested from c. 1300, also "aloof, reserved, distant; estranged." In nuclear physics, from 1956.
late 14c., alienacioun, "action of estranging, disownment;" early 15c., "transfer of one's title to property or rights," 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." This is 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.