Definition of flails:
(v) :
(transitive) To wave or swing vigorously
(v) :
(transitive) To beat using a flail or similar implement.
(v) :
(intransitive) To move like a flail.
(n) :
A tool used for threshing, consisting of a long handle (handstock) with a shorter stick (swipple or swingle) attached with a short piece of chain, thong or similar material.
(n) :
A weapon which has the (usually spherical) striking part attached to the handle with a flexible joint such as a chain.
(v) :
(transitive) To thresh.