Monkey appearing in section of wall (7)
I believe the answer is:
parapet
'wall' is the definition.
(thesaurus)
'monkey appearing in section' is the wordplay.
'monkey' becomes 'ape' (I've seen this before).
'appearing in' is an insertion indicator.
'section' becomes 'part' ('part' can be a synonym of 'section').
'ape' put within 'part' is 'PARAPET'.
'of' is the link.
(Other definitions for parapet that I've seen before include "Low wall (on bridge, roof, etc)" , "low bank" , "Fortification consisting of a low wall" , "Defensive wall" , "form of protection" .)