Back issue by Sunday paper (5)
I believe the answer is:
times
'paper' is the definition.
(The Times newspaper)
'back issue by sunday' is the wordplay.
'back' says the letters should be written in reverse.
'issue' becomes 'emit' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'sunday' becomes 's'.
'emit' written backwards gives 'time'.
'time'+'s'='TIMES'
(Other definitions for times that I've seen before include "Periods, ages" , "''For the ..., they are a'changin'''(Bob Dylan)" , "measures the length of something" , "Paper" , "Paces" .)