Strengthen a delicate fabric (4)
I believe the answer is:
lace
I believe this is a double definition.
'strengthen' is the first definition.
(thesaurus)
'a delicate fabric' is the second definition.
(I've seen this before)
(Other definitions for lace that I've seen before include "Spike - ornamental fabric" , "Famous play ''Arsenic and Old . . . .''" , "Delicate open-weave fabric" , "Do up (shoe, etc)" , "Delicate material" .)