a bread-and-butter letter
A thank-you note to one's host. Now that you're back from your stay with Auntie Jean, be sure to write her a bread-and-butter letter.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a letter or note written to follow up on a visit; a thank-you note. When I got back from the sales meeting, I took two days to write bread-and-butter letters to the people I met. I got sort of a bread-and-butter letter from my nephew, who wants to visit me next summer.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.