Appropriate part of harness (7)
I believe the answer is:
snaffle
I believe this clue is a double definition.
'appropriate' is the first definition.
(I've seen this before)
'harness' is the second definition.
(thesaurus)
'part of' acts as a link.
(Other definitions for snaffle that I've seen before include "Appropriate" , "Capture" , "Pinch" , "bit for the horse" , "Get hold of" .)