Source : Webster's Revised Unabridged Dictionary (1913)

Ace \Ace\, n.; pl. {Aces}. [OE. as, F. as, fr. L. as, assis,
   unity, copper coin, the unit of coinage. Cf. {As}.]
   1. A unit; a single point or spot on a card or die; the card
      or die so marked; as, the ace of diamonds.

   2. Hence: A very small quantity or degree; a particle; an
      atom; a jot.

            I 'll not wag an ace further.         --Dryden.

   {To bate an ace}, to make the least abatement. [Obs.]

   {Within an ace of}, very near; on the point of. --W. Irving.