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
LÉOnce	-	French
Cronus	KRO-nəs (English)	Greek Mythology (Latinized)
Tacitus	-	Ancient Roman
Kennedy	KEN-ə-dee	English, Irish
Lottie	-	English, Swedish
Aerona	-	Welsh