Soldier-turned-aristocrat is contemptible (7)
I believe the answer is:
ignoble
'contemptible' is the definition.
(similar in meaning)
'soldier-turned-aristocrat' is the wordplay.
'soldier' becomes 'GI' (term for US soldier).
'turned' says the letters should be written in reverse.
'aristocrat' becomes 'Noble' (member of the nobility).
'gi' back-to-front is 'ig'.
'ig'+'noble'='IGNOBLE'
'is' is the link.
(Other definitions for ignoble that I've seen before include "Wretched, base" , "Inferior" , "No bilge! (anag)" , "'Base, dishonourable (7)'" , "'Far from the madding crowd's . . . . . . . strife'" .)