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
Sharifa	-	Arabic
Ljilja	-	Serbian
RafaŁ	RAH-fow	Polish
Maybelline	-	English (Rare)
Pia	PEE-ah (Italian, Danish, German)	Italian, Swedish, Norwegian, Danish, German, Polish, Slovene, Late Roman
MarÍA	mah-REE-ah (Spanish)	Spanish, Galician, Icelandic