1721, from verb naysay (implied from 1530s in naysaying); from nay + say (v.). Nay-say "refusal" is from 1630s.[naysayer etymology, naysayer origin, 英语词源]
mid-14c., zoþ ziggere (Kentish), "one who speaks truth,;" late 14c., sothseggere, "fortune-teller;" see sooth + say. Old English had soðsagu "act of speaking the truth."