Definition of "thrasher"

One who thrashes.  examples

Any of several New World passerine songbirds, of the genera Toxostoma, Allenia, Margarops, Oreoscoptes and Ramphocinclus in the family Mimidae, that have a long, downward-curved beak.  examples

A thresher shark.  examples

(informal) A fan of thrash metal music.  examples