Dear John

noun Informal.

a letter from a woman informing her boyfriend or fiancé that she is ending their relationship or informing her husband that she wants a divorce: Nothing is worse for a soldier's morale than getting a Dear John.
any letter terminating a relationship.

Origin of Dear John

First recorded in 1940–45

Also called Dear John letter.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for dear john letter

Dear John letter

noun

informal a letter from someone (esp to a man) breaking off a love affair

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012