Soldier on favourite barricade (7)
I believe the answer is:
parapet
'barricade' is the definition.
(thesaurus)
'soldier on favourite' is the wordplay.
'soldier' becomes 'para' (paratrooper).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'favourite' becomes 'pet' (synonyms).
'para'+'pet'='PARAPET'
(Other definitions for parapet that I've seen before include "Wall's top" , "Low wall (on bridge, roof, etc)" , "defensive position" , "Low wall along the side of a bridge" , "part of castle" .)