Source : Webster's Revised Unabridged Dictionary (1913)

Yes \Yes\, adv. [OE. yis, [yogh]is, [yogh]es, [yogh]ise, AS.
   gese, gise; probably fr. ge['a] yea + sw[=a] so. [root]188.
   See {Yea}, and {So}.]
   Ay; yea; -- a word which expresses affirmation or consent; --
   opposed to {no}.

   Note: Yes is used, like yea, to enforce, by repetition or
         addition, something which precedes; as, you have done
         all this -- yes, you have done more. ``Yes, you despise
         the man books confined.'' --Pope.

   Note: ``The fine distinction between `yea' and `yes,' `nay'
         and `no,' that once existed in English, has quite
         disappeared. `Yea' and `nay' in Wyclif's time, and a
         good deal later, were the answers to questions framed
         in the affirmative. `Will he come?' To this it would
         have been replied, `Yea' or `Nay', as the case might
         be. But, `Will he not come?' To this the answer would
         have been `Yes' or `No.' Sir Thomas More finds fault
         with Tyndale, that in his translation of the Bible he
         had not observed this distinction, which was evidently
         therefore going out even then, that is, in the reign of
         Henry VIII.; and shortly after it was quite
         forgotten.'' --Trench.

Source : WordNet®

yes
     n : an affirmative; "I was hoping for a yes" [ant: {no}]