flail 
(flāl)
(flāl)n.
A manual threshing device consisting of a long wooden handle or staff and a shorter, free-swinging stick attached to its end.
v. flailed, flail·ing, flails
v.tr.
1. To beat or strike with or as if with a flail: flailed our horses with the reins.
2. To wave or swing vigorously; thrash: flailed my arms to get their attention.
3. To thresh using a flail.
v.intr.
1. To move vigorously or erratically; thrash about: arms flailing helplessly in the water.
2. To strike or lash out violently: boxers flailing at each other in the ring.
3. To make energetic but aimless or or ineffectual efforts: "As the end of law school approached, Hill flailed briefly in numerous professional directions" (Molly Worthen).
4. To thresh grain.
[Middle English, from Old English flegil and from Old French flaiel, both from Late Latin flagellum, threshing tool, from Latin flagrum, whip.]