ace up one's sleeve

Etymology
From the dishonest hiding of a high-value ace card for use during play, e.g. in the game of poker.

Noun

 * 1)  A surprise advantage of which others are not aware.

Translations

 * Chinese:
 * Cantonese: 秘密王牌
 * Hokkien: 秘密王牌
 * Mandarin: 秘密王牌
 * Czech: Eso v rukávu
 * Estonian: Trump tagataskust
 * Finnish: ässä hihassa
 * French:, as dans la manche, atout dans la manche, avoir un atout dans sa manche, garder un atout dans sa manche
 * German: Ass im Ärmel, Trumpf im Ärmel
 * Italian: asso nella manica
 * Japanese: ,
 * Norwegian: ess i ermet
 * Polish: as w rękawie
 * Portuguese: carta nas mangas,
 * Russian:, туз в рукаве́, козы́рна́я ка́рта
 * Serbo-Croatian: кец у рукаву
 * Spanish: as en la manga, as bajo la manga
 * Swedish: äss i rockärmen