One held in custody (8)
I believe the answer is:
detainee
'one held in custody' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for detainee that I've seen before include "One is held under guard, for political reasons perhaps" , "One penned" , "One held in custody" , "Someone held in custody" , "confined person" .)