c. 1300, "appearance from which inferences may be drawn," from Old French evidence, from Late Latin evidentia "proof," in classical Latin "distinction, vivid presentation, clearness" in rhetoric, from stem of Latin evidens "obvious, apparent" (see evident).
Meaning "ground for belief" is from late 14c.; that of "obviousness" is from 1660s and tacks closely to the sense of evident. Legal senses are from c. 1500, when it began to oust witness. Also "one who furnishes testimony, witness" (1590s); hence turn (State's) evidence.