Sort of interest in enclosure (8)
I believe the answer is:
compound
I believe this clue is a double definition.
'sort of interest' is the first definition.
'enclosure' is the second definition.
(I know that compound is a type of enclosure)
'in' acts as a link.
(Other definitions for compound that I've seen before include "Whole formed by separate elements" , "A mix of ingredients" , "Enclosed area - not simple!" , "Kind of interest accumulating on capital plus interest" , "Fenced area; chemical substance" .)