Bit of thatching (4)
I believe the answer is:
reed
'bit of thatching' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reed that I've seen before include "Type of musical instrument" , "Vibrating part of some instruments" , "Marsh plant with tall straight stem" , "Blade of tall marsh grass" , "ancient arrow" .)