Stratagem is a noun that refers to a move made to outwit one's opponents.

The Greek word stratos (STRAH tose) means ‘army.’ This gave birth to a number of words like ‘strategy’ that originated in military use, but can be used outside of that context as well. Stratagem refers specifically to a move made to fool an enemy.

Chuck’s decision to go to the bathroom in the middle of the poker game was probably a scheme to help him win the game. He’s always devising these weird stratagems when he really should be focusing on playing a better game.