Work on a sweater (4)
I believe the answer is:
knit
'work on a sweater' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for knit that I've seen before include "Fuse" , "Use needles to make clothes" , "Tighten (eyebrows) in a frown; unite" , "tie" , "Use needles and wool" .)