Thatcher may have used these instruments (5)
I believe the answer is:
reeds
'these instruments' is the definition.
(reed is a kind of instrument)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for reeds that I've seen before include "River grasses" , "Music-makers" , "Marsh plants with tall straight stems" , "Thatching stalks" , "Tall grasses with hollow stems" .)