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."