Question: Why is a tennis score of 40-40 called "deuce"?
Answer: Ancient civilizations in Rome, Greece and Egypt have made claim to the sport's origins, but what we recognize today as tennis is widely accepted to have begun in France. Where else but in the land of romance would athletic measure be articulated in the terms "love" and "deuce" (as in, it takes two)?
During the Middle Ages, French monks hit balls with their hands over a rope stretched across the cloistered quadrangles of their monasteries. What they called jeu de paume (palm game) evolved into "tennis" courtesy of the serving player, who initiated action by shouting "Tenez!" -- roughly, "Take it!"
In the game's incrementally peculiar scoring, the first point is 15 (or 5, if the players went to prep school), the next is 30, the third, 40, then game over, provided the winning margin is two points. Players can be tied at 15 and at 30, but not beyond; 40-all is deemed "deuce" because it is a "deux du jeu" -- two points away from winning the game.