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.

Source: Webster's Revised Unabridged Dictionary (1913)