ace up (one's) sleeve

A secret advantage. My stamina is the ace up my sleeve for this race—the other runners don't stand a chance! The defense attorney waited for just the right time to play the ace up her sleeve—a new eye-witness.

Common Names:

Name	Pronounced	Usage
Elowen	-	Cornish
Darcy	['dɑ:si]
Bobbie	['bɔbi]
Winter	['wintə]
Jamshid	-	Persian, Persian Mythology
Maud	[mɔd]