Enormous soldier -- a six-footer (5)
I believe the answer is:
giant
'enormous' is the definition.
(thesaurus)
'soldier a six-footer' is the wordplay.
'soldier' becomes 'gi' (government issue or general issue**).
'a six footer' becomes 'ant' (an ant has six feet).
'gi'+'ant'='GIANT'
(Other definitions for giant that I've seen before include "Huge; James Dean film" , "A mighty man like Goliath or Carnera" , "Ogre" , "Colossus" , "Extremely tall person" .)