Ductwork sealer (4)
I believe the answer is:
tape
'ductwork sealer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tape that I've seen before include "Sticky strip" , "Common medium for recording" , "Fabric strip; record" , "Music cassette" , "Breast this first to win a race" .)