New cadet played a part (5)
I believe the answer is:
'played a part' is the definition.
(I've seen this before)
'new cadet' is the wordplay.
'new' indicates an anagram.
'cadet' with letters rearranged gives 'ACTED'.
(Other definitions for acted that I've seen before include "Feigned" , "Posed as" , "Took part in play" , "produced an effect" , "Cadet (anag)" .)