Concert attended by old knight (conservative) in cape (10)
I believe the answer is:
promontory
'cape' is the definition.
(thesaurus)
'concert attended by old knight conservative' is the wordplay.
'concert' becomes 'prom' (abbreviation for promenade concert).
'attended by' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'knight' becomes 'n' (chess).
'conservative' becomes 'tory' (informal term for a Conservative Party member).
'prom'+'o'+'n'+'tory'='PROMONTORY'
'in' is the link.
(Other definitions for promontory that I've seen before include "Headland" , "Coastal feature" , "Bluff" , "Head" , "Bill" .)