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
Nagore	-	Basque
Azaziah	-	Biblical
Sebastian	ze-BAHS-tee-ahn (German), sə-BAS-chən (English), se-BAHS-tyahn (Polish), SE-bahs-tee-ahn (Finnish)	German, English, Swedish, Norwegian, Danish, Polish, Finnish, Romanian
Humphry	HUM-free	English (Rare)
&Thorn;ÓRr	-	Norse Mythology
Eli (2)	-	Hebrew