We found 2 dictionaries that define the word scratch someone's back:

General (2 matching dictionaries)

1. scratch someone's back: Merriam-Webster
2. scratch someone's back: Wiktionary

Definitions from Wiktionary (scratch someone's back) ▸ verb:  (informal) To do someone a favour. ▸ Words similar to scratch someone's back ▸ Usage examples for scratch someone's back ▸ Idioms related to scratch someone's back ▸ Wikipedia articles (New!) ▸ Words that often appear near scratch someone's back ▸ Rhymes of scratch someone's back ▸ Invented words related to scratch someone's back