Matching cardigan and jumper (7)
I believe the answer is:
twinset
'matching cardigan and jumper' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for twinset that I've seen before include "Matching cardigan and jumper when worn at the same time" , "Kit worn to match" , "clothing" , "Wear associated with pearls?" , "Matching cardigan and jumper worn together" .)