Bit of thatch (4)
I believe the answer is:
reed
'bit of thatch' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for reed that I've seen before include "Tall grass plant that grows in water" , "Carol" , "Tall grass of wet areas" , "Blade of tall marsh grass" , "Marsh plant for deer" .)