Gun man saying Rebecca used him? (5)

I believe the answer is:
maxim
I believe this clue is a quadruple definition!!
'gun' is the first definition.
(thesaurus)
'man' is the second definition.
'saying rebecca' is the third definition.
'maxim' can be an answer for 'saying' (I've seen this before). I am not certain of the 'rebecca' bit.
'used' is a link.
'him?' is the fourth definition.
Can you help me to learn more?
(Other definitions for maxim that I've seen before include "Short pithy saying" , "Saying, adage" , "Saying - inventor of machine gun" , "Pithy statement of a general truth" , "Widely accepted saying" .)
