How did the word "love" come to mean zero in the game of tennis?
Although tennis historians aren't sure exactly how the term "love" came to mean zero in tennis, the most plausible assumption seems to be that it's based on the French word "l'oeuf."
Court tennis, an ancestor of most of today's racket games, originated in 14th century France. Pronounced correctly "l'oeuf"—meaning "egg"—sounds similar to "love." And the egg, which unquestionably looks like a zero, could have been used to describe a zero written on a scoreboard.
—The Fact Monster