Some cadet erring, put off (5)
I believe the answer is:
deter
'put off' is the definition.
(both can mean to discourage)
'some cadet erring' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'DETER' is hidden in the letters of 'cadet erring'.
(Other definitions for deter that I've seen before include "stop" , "Warn off" , "Discourage (an activity)" , "Check" , "Put (someone) off" .)