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.
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Idioms and Phrases with 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
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