Rogue extraterrestrial who may become an officer! (5)
I believe the answer is:
cadet
'officer' is the definition.
(I have seen 'Potential officer ' mean 'cadet' so perhaps 'officer' could also mean 'cadet')
'rogue extraterrestrial' is the wordplay.
'rogue' becomes 'cad' (I've seen this in another clue).
'extraterrestrial' becomes 'et' (I've seen this in other clues).
'cad'+'et'='CADET'
'who may become an' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for cadet that I've seen before include "Younger member of family" , "Police force trainee" , "Tomboy" , "Trainee -- acted (anag)" , "Officer in training" .)