Is it farther or further?
c.1300, "appearance from which inferences may be drawn," from Old French evidence, from Late Latin evidentia "proof," originally "distinction, clearness," from Latin evidentem (see evident).
Meaning "ground for belief" is from late 14c., that of "obviousness" is 1660s. Legal senses are from c.1500, when it began to oust witness. As a verb, from c.1600. Related: Evidenced; evidencing.