Sickness in jail mentioned (7)
I believe the answer is:
ailment
'sickness' is the definition.
(I know that sickness can be written as ailment)
'in jail mentioned' is the wordplay.
'in' indicates the answer is hidden within the clue.
'AILMENT' is hidden in the letters of 'jail mentioned'.
(Other definitions for ailment that I've seen before include "Physical disorder" , "I lament (anag.)" , "Minor illness" , "Sickness" , "Bodily disorder or disease" .)