Source : Webster's Revised Unabridged Dictionary (1913)

Nay \Nay\, adv. [Icel. nei; akin to E. no. See {No}, adv.]
   1. No; -- a negative answer to a question asked, or a request
      made, now superseded by no. See {Yes}.

            And eke when I say ``ye,'' ne say not ``nay.''
                                                  --Chaucer.

            I tell you nay; but except ye repent, ye shall all
            likewisr perish.                      --Luke xiii.
                                                  3.

            And now do they thrust us out privily? nay, verily;
            but let them come themselves and fetch us out.
                                                  --Acts xvi.
                                                  37.

            He that will not when he may, When he would he shall
            have nay.                             --Old Prov.

   Note: Before the time of Henry VIII. nay was used to answer
         simple questions, and no was used when the form of the
         question involved a negative expression; nay was the
         simple form, no the emphatic. --Skeat.

   2. Not this merely, but also; not only so, but; -- used to
      mark the addition or substitution of a more explicit or
      more emphatic phrase.

   Note: Nay in this sense may be interchanged with yea. ``Were
         he my brother, nay, my kingdom's heir.'' --Shak.

Nay \Nay\, n.; pl. {Nays}.
   1. Denial; refusal.

   2. a negative vote; one who votes in the negative.

   {It is no nay}, there is no denying it. [Obs.] --haucer.

Nay \Nay\, v. t. & i.
   To refuse. [Obs.] --Holinshed.

Source : WordNet®

nay
     n : a negative; "the nays have it" [ant: {yea}]
     adv : not this merely but also; not only so but; "each of us is
           peculiar, nay, in a sense unique"