Trainee soldier from America detained (5)
I believe the answer is:
cadet
'trainee soldier' is the definition.
(I've seen this before)
'from america detained' is the wordplay.
'from' indicates a hidden word.
'CADET' can be found hidden inside 'america detained'.
(Other definitions for cadet that I've seen before include "who needs to be properly trained?" , "Junior officer; younger brother" , "Potential officer" , "Trainee cop" , "not the heir" .)