The set number fed out (5)
I believe the answer is:
fixed
'the set' is the definition.
(I've seen this before)
'number fed out' is the wordplay.
'number' becomes 'ix' (IX is an example).
'out' means one lot of letters goes inside another.
'ix' put inside 'fed' is 'FIXED'.
(Other definitions for fixed that I've seen before include "Repaired" , "Securely fastened" , "Arranged" , "Established" , "Set" .)