Belle is from the French belle (beautiful) — the feminine form of beau. *"La Belle" — "Beauty" — is the heroine of the French fairy tale La Belle et la Bête (Beauty and the Beast) first published by Gabrielle-Suzanne Barbot de Villeneuve in 1740; Jeanne-Marie Leprince de Beaumont's 1756 abridged version is the version most commonly read today. Disney's animated Beauty and the Beast (1991) was the first animated film nominated for Best Picture at the Academy Awards; the live-action 2017 remake with Emma Watson became one of the highest-grossing films of 2017. Belle Boyd (1844-1900) — Confederate spy during the American Civil War. Belle Starr (1848-1889) — American outlaw. A top-1000 US baby name from 1880 through 1934 and again from 2011 to present*.
Subject of Jean Cocteau's La Belle et la Bête (1946 film) and Bill Condon's 2017 live-action remake.
In Pythagorean numerology the letters of Belle reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.