Is imprisoned by key and lock, suffering (8)
I believe the answer is:
distress
'suffering' is the definition.
('distress' can be a synonym of 'suffering')
'is imprisoned by key and lock' is the wordplay.
'imprisoned by' means one lot of letters goes inside another.
'key' becomes 'd' (I've seen this in other clues).
'and' is a charade indicator (letters next to each other).
'lock' becomes 'tress' (I've seen this before).
'd'+'tress'='dtress'
'is' inserted inside 'dtress' is 'DISTRESS'.
(Other definitions for distress that I've seen before include "Severe pain" , "Peril" , "State of suffering" , "Suffering, worry" , "Mayday is such a signal." .)