Soldier atop favourite defensive wall (7)
I believe the answer is:
parapet
'defensive wall' is the definition.
(I've seen this in another clue)
'soldier atop favourite' is the wordplay.
'soldier atop' becomes 'para' (short for paratrouper. I am not sure about the 'atop' bit.).
'favourite' becomes 'pet' (synonyms).
'para'+'pet'='PARAPET'
Can you help me to learn more?
(Other definitions for parapet that I've seen before include "form of defence" , "Low barrier edging balcony" , "works" , "Defensive wall" , "part of castle" .)