Idioms and Phrases with bread-and-butter letter
A thank-you letter from guest to host. For example, Mother always had to remind the children to send Grandma a bread-and-butter note. [c. 1900]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.