Male breaking in to knock off old cape (6)
I believe the answer is:
domino
'cape' is the definition.
(thesaurus)
'male breaking in to knock off old' is the wordplay.
'male' becomes 'm' (common abbreviation).
'breaking in' means one lot of letters goes inside another.
'to knock off' becomes 'doin' (both can mean to murder).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'm' inserted within 'doin' is 'domin'.
'domin'+'o'='DOMINO'
(Other definitions for domino that I've seen before include "garment" , "Small block with dots for table game" , "Rectangular tile (with an effect?) used in a table game" , "Piece with pips; Fats ---, R&B singer" , "such a falling effect" .)