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
Na'im	-	Arabic
Narges	-	Persian
Patience	['peiʃəns]
Marcelo	mahr-THE-lo (Spanish), mahr-SE-lo (Latin American Spanish)	Spanish, Portuguese
Aldegund	-	Ancient Germanic
Bernardita	-	Spanish