Thresh about (5)
I believe the answer is:
flail
'thresh about' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for flail that I've seen before include "Threshing device" , "Thresher; wave helplessly about" , "Grain thresher" , "Threshing implement" , "Old tool for threshing grain" .)