Callow recruit (6)
I believe the answer is:
rookie
'callow recruit' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rookie that I've seen before include "Slang for a new recruit" , "inexperienced fighter" , "New recruit as to army" , "New (police) recruit (colloq.)" , "Callow recruit" .)