Fix hose (4)
I believe the answer is:
'fix hose' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for darn that I've seen before include "Mend by stitching - damn!" , "Sew" , "Blow" , "Repair by sewing, socks perhaps" , "Mend with 17s - mild expletive" .)