Reformed inmate receiving long complaint (7)
I believe the answer is:
ailment
'complaint' is the definition.
(I know that complaint can be written as ailment)
'reformed inmate receiving long' is the wordplay.
'reformed' indicates anagramming the letters.
'receiving' indicates putting letters inside.
'long' becomes 'l'.
'inmate' is an anagram of 'aiment'.
'aiment' placed around 'l' is 'AILMENT'.
(Other definitions for ailment that I've seen before include "Slight but persistent illness" , "Tummy upset, for instance" , "Complaint, affliction" , "Tim Alen has an odd indisposition." , "Sickness" .)