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tooth fairy

noun

a fairy credited with leaving a child money or a small gift in exchange for a baby tooth that has fallen out and been placed under the child's pillow at night.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Idioms and Phrases with tooth fairy

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.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.