Collide with section as part of defence (7)
I believe the answer is:
rampart
'defence' is the definition.
(I know that rampart is a type of fortification)
'collide with section as' is the wordplay.
'collide' becomes 'ram' (ramming is a kind of colliding).
'with' means one lot of letters go next to another.
'section as' becomes 'part' (synonyms. I am not sure about the 'as' bit.).
'ram'+'part'='RAMPART'
'part of' is the link.
Can you help me to learn more?
(Other definitions for rampart that I've seen before include "Defensive wall or mound" , "Castle embankment" , "barricade" , "Defensive structure" , "Broad defensive wall" .)