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.
Also called
Dear John letter.
Origin of Dear John
First recorded in 1940–45
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