1. The face of a die that bears two spots
2. A playing card bearing an index number two
3. A throw of the dice yielding two points
4. [obsolete English deuce bad luck] Devil, dickens — used chiefly as a mild oath; something notable of its kind
5. One of four cards in a deck having two spots.

A tie in tennis after each side has scored 40 requiring two consecutive points by one side to win

To bring the score of (a tennis game or set) to deuce.