Primate in role, as protection against the enemy? (7)
I believe the answer is:
parapet
'protection against the enemy?' is the definition.
'primate in role' is the wordplay.
'primate' becomes 'ape' (I've seen this before).
'in' means one lot of letters goes inside another.
'role' becomes 'part' ('part' can be a synonym of 'role').
'ape' going inside 'part' is 'PARAPET'.
'as' acts as a link.
(Other definitions for parapet that I've seen before include "Low barrier edging balcony" , "Rooftop wall" , "Defensive line" , "Wall, a low sort" , "Wall's top" .)