Criminal suffering, say, jail regularly (7)
I believe the answer is:
illegal
'criminal' is the definition.
('illegal' can be similar in meaning to 'criminal')
'suffering say jail regularly' is the wordplay.
'suffering' becomes 'ill'.
'say' becomes 'eg'.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'jail' are 'al'.
'ill'+'eg'+'al'='ILLEGAL'
(Other definitions for illegal that I've seen before include "Contrary to law" , "Felonious" , "Unlawful" , "Criminal, illicit" , "Black" .)