"Matched" collection (3)
I believe the answer is:
set
'matched collection' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for set that I've seen before include "Arrange; a party" , "Gel; start (a fire)" , "'Put, place or fix in position (3)'" , "carriage" , "Scenery for play or film" .)