Military assistant (4)
'military assistant' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aide that I've seen before include "Military officer acting as assistant" , "Second" , "Personal assistant in the military" , "Helper" , "One to assist" .)
(Other definitions for adjutant that I've seen before include "CO's aide" , "Administrative assistant to commanding officer" , "Officer's assistant" , "one with large bill" , "Military admin officer" .)