The origins of the 15, 30, 40 and so on are not known, but are thought to have medieval and French roots. One possible explanation is that the scoring system is based on the presence of a clock face at the end of the tennis court. A quarter move of the appropriate hand was made after each rest, with the score being called as 15, 30, or 45 as the case might be. When the hand moved to 60, the circuit was completed and so was the game.
The term "deuce" is derived from the French "deux", where an advantage of two points has to be gained. "Love" is generally taken as being derived from the French "l"oeuf", the egg, symbolising nothing. It has also been claimed that the term "love" comes from the English phrase "neither for love nor for money", i.e., for nothing.