mid-15c., "do an injustice to, dishonor," probably a back-formation from injury, or else from Old French injuriier "to damage; offend," from Latin iniuriari "do an injury," from iniuria. Injury itself also served as a verb meaning "to injure, hurt, harm" (late 15c.). Related: Injured; injuring.
in-joke
injudicious
Injun
injunction
injunctive
injure
injurious
injury
injustice
ink
inkhorn