pistachio n.

1590s, "nut of the pistachio tree," from Italian pistacchio, from Latin pistacium "pistachio nut," from Greek pistakion "pistachio nut," from pistakē "pistachio tree," from Persian pistah "pistachio." Borrowed earlier in English as pystace, pistace (mid-15c.), from Old French pistace (13c.) and Medieval Latin pistacia, ultimately from the same source.