Women inside can fix matching garments (7)
I believe the answer is:
twinset
'matching garments' is the definition.
(I've seen this before)
'women inside can fix' is the wordplay.
'women' becomes 'w' (standard abbreviation).
'inside' means one lot of letters goes inside another.
'can' becomes 'tin' (synonyms).
'fix' becomes 'set' (synonyms).
'w' put inside 'tin' is 'twin'.
'twin'+'set'='TWINSET'
(Other definitions for twinset that I've seen before include "Matching cardigan and jumper worn together" , "clothing" , "Matching garments" , "Matching cardigan and jumper when worn at the same time" , "Kit worn to match" .)