tooth fairy
1. A mythical fairy that exchanges money for children's baby teeth that have fallen out and been placed beneath their pillow at night. My sister believed in the tooth fairy until she was nearly 15. Look, Mom! The tooth fairy left me a whole dollar for my molar last night!
2. Any mythical benefactor or source of money. The tooth fairy isn't going to come along and fund this project for us.
tooth fairy
A mythical source of bounty, as in So who will finance this venture-the tooth fairy? This expression refers to the fairy credited with leaving money under a child's pillow in place of a baby tooth that has fallen out, a practice popular with American parents since the first half of the 1900s.