1620s, possibly via 16c. Italian ingraziarsi "to bring (oneself) into favor," or an unrecorded Medieval Latin *ingratiatus, from Latin phrase in gratiam "for the favor of," from in "in" (from PIE root *en "in") + gratia "favor, grace" (from suffixed form of PIE root *gwere- (2) "to favor"). Related: Ingratiated; ingratiating.
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Definitions of ingratiation from WordNet
the act of gaining acceptance or affection for yourself by persuasive and subtle blandishments;