Why is a zero score called 'love' in tennis?
A popular guess is the French 'l'oeuf', an egg shaped like a zero, but evidence is thin.
No one has proved why a zero score is called love, and reference works treat the common explanations as theories. The most repeated one says the word comes from French l'oeuf, the egg, because a zero looks like an egg. It is plausible by analogy with cricket, where a zero is a duck, short for duck's egg, but there is no firm evidence of the French phrase ever being used for tennis scoring.
Another proposal is that love derives from the idea of playing for love of the game, meaning with nothing at stake but pride, so the player with no points is playing only for love. A related suggestion points to a Dutch phrase meaning to do something for praise. Dictionaries record the English term in sport from the eighteenth century, so it is old, but the first uses do not explain it.
The rest of tennis scoring is also uncertain. The sequence 15, 30, 40 has been linked to a clock face with the 45 shortened to 40, and deuce to the French à deux, but these accounts are also unproven. Because the sport evolved from the medieval French jeu de paume, and terms were borrowed and altered by English speakers, the trail of evidence is thin. Honest answers to the question therefore stay at the level of competing theories.