A back numbers issue (3)
I believe the answer is:
son
'issue' is the definition.
(issue can mean someone's offspring)
'a back numbers' is the wordplay.
'a back' says the letters should be written backwards.
'numbers' becomes 'nos' ('no' is an abbreviation for number).
'nos' written backwards gives 'SON'.
(Other definitions for son that I've seen before include "Male child" , "A relative" , "Heir" , "Male descendant" , "Human offspring" .)