Ace/eɪs/ Definition 1 of 5Pro Tip 1/2Card Games Reference Understand that 'ace' is often used in idioms meaning a secret advantage. He has an ace up his sleeve in negotiations. Pro Tip 2/2Cultural Symbolism The 'ace of spades' can symbolize good luck or death, depending on the context. In some stories, finding an ace of spades is an ominous sign.