Sew harness (4)
I believe the answer is:
tack
I believe this clue is a double definition.
'sew' is the first definition.
(thesaurus)
'harness' is the second definition.
(thesaurus)
(Other definitions for tack that I've seen before include "Cheap material; nail" , "Nail for carpet?" , "Poor food" , "Nail - windward course - temporary stitch" , "vulgar" .)