Old soldier supine ultimately in tavern, drunk (7)
I believe the answer is:
veteran
'old soldier' is the definition.
(thesaurus)
'supine ultimately in tavern drunk' is the wordplay.
'ultimately' suggests the final letters.
'in' indicates putting letters inside.
'drunk' indicates an anagram.
The final letter of 'supine' is 'e'.
'tavern' anagrammed gives 'vetran'.
'e' inserted inside 'vetran' is 'VETERAN'.
(Other definitions for veteran that I've seen before include "he's seen a lot of service" , "Experienced ex-serviceman" , "Retired soldier" , "American ex-soldier or old hand" , "Warhorse" .)