thresh / [unvoicedth]resh/ • v. [tr.] 1. separate grain from (a plant), typically with a flail or by the action of a revolving mechanism: machinery that can reap and thresh corn in the same process | [as n.] (threshing) farm workers started the afternoon's threshing.2. variant spelling of thrash (in the sense of violent movement).
Hence thresher (-ER1) person or machine that threshes XIV; shark so named from the upper division of its tail with which it lashes an enemy XVII.