Definition of Dear John letter in English:
 Dear John letter
(also Dear John)
noundɪə ˈdʒɒn lɛtədɪəˈdʒɒnletə(r)
informal A letter from a woman to a man, ending a romantic or sexual relationship.
 a young officer gets his Dear John letter
 Example sentencesExamples
-  I told her ‘You sent me a Dear John letter in 1949’.
 -  My girlfriend of four years had sent me a "Dear John" letter, saying she had waited too long for me to return and found someone else.
 -  You might think it's easier this way but have you though about how many suicides are caused in direct response to a receiving a Dear John Letter?
 -  Soldiers mourn their friends, and bemoan Dear John letters.
 -  There isn't a love note, Dear John letter or other outpouring of amorous intention that I haven't seen or perpetrated by now.