Opponent

An opponent was a person or team that one could compete against in a game, sport, or debate.

In 2367, Data noted in his second officer's personal log that "In the game of poker, there is a moment when a player must decide if an opponent is being deceptive or actually holds a winning hand. This decision is based not only on the odds, but also on an appraisal of the man – is he bluffing or does he have the cards?" (TNG: "Data's Day")