1548, "make estranged" (in feelings or affections), from L.
alienatus, pp. of
alienare "to make another's, estrange," from
alienus "of or belonging to another person or place," from
alius "(an)other" (see
alias).
Alienation in the sense of "transfer of ownership" is from 1388; it also meant "loss or derangement of mental faculties, insanity" (1482), hence
alienist (1864, from Fr.
aliéniste) "one who treats mental diseases."
Alienation of affection as a U.S. legal term in divorce cases for "falling in love with someone else" is from 1861.