late 14c., from Old French injustice "unfairness, injustice" (14c.), from Latin iniustitia "unfairness, injustice," from iniustus "unjust, wrongful, unreasonable, improper, oppressive," from in- "not" (see in- (1)) + iustus "just" (see just (adj.)). Injust (adj.) is attested from late 15c., from French, but unjust is the usual English word.
