Wife cheating endlessly (4)
I believe the answer is:
frau
'wife' is the definition.
(Frau is an example)
'cheating endlessly' is the wordplay.
'cheating' becomes 'fraud'.
'endlessly' means to remove the last letter.
'fraud' with its last letter removed is 'FRAU'.
(Other definitions for frau that I've seen before include "Married German-speaking woman" , "German woman's title" , "German wife" , "Mrs in Germany" , "German title for a woman" .)