French word in- comes from Latin ingratus (Thankless. Ungrateful. Unpleasant, disagreeable.), French in- (In-; un- (indicates negation).)

Detailed word origin of in-

Dictionary entry	Language	Definition
ingratus	Latin (lat)	Thankless. Ungrateful. Unpleasant, disagreeable.
in-	French (fra)	In-; un- (indicates negation).

Words with the same origin as in-