The unit of cards or dice, from as>, the Latin
unit of weight. (Italian, asso; French and Spanish, as.)
Within an ace.
Within a shave. An ace is the lowest numeral, and he who wins
within an ace, wins within a single mark. (See Ambes-As.)
To bate an ace
is to make an abatement, or to give a competitor some start or
other advantage, in order to render the combatants more equal. It said
that the expression originated in the reign of Henry VIII, when one of
the courtiers named Bolton, in order to flatter the king, used to say
at cards, “Your Majesty must bate me an ace, or I shall have no chance
at all.” Taylor, the water poet (1580–1654), speaking of certain
Though bad they be, they will not bate an ace
To be cald Prudence, Temprance, Faith, and Grace.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894