Shoestring (4)
I believe the answer is:
lace
'shoestring' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lace that I've seen before include "Delicate open-web fabric" , "Spike - ornamental fabric" , "Shoe tie" , "A fabric; add alcohol to" , "Flimsy fabric or shoe fasterner" .)