Old soldier (7)
I believe the answer is:
veteran
'old soldier' is the definition.
(veteran can mean a former soldier)
This is all the clue.
(Other definitions for veteran that I've seen before include "Nervate (anag.)" , "An old hand or ex-soldier in USA" , "One of great experience" , "Describing cars built before 1919, especially before 1905" , "Person with long experience, as in American army" .)