flail vs thrasher

flail

noun
  • A weapon which has the (usually spherical) striking part attached to the handle with a flexible joint such as a chain. 

  • A tool used for threshing, consisting of a long handle with a shorter stick attached with a short piece of chain, thong or similar material. 

verb
  • To beat using a flail or similar implement. 

  • To wave or swing vigorously 

  • To thresh. 

  • To move like a flail. 

thrasher

noun
  • One who thrashes. 

  • 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. 

  • A fan of thrash metal music. 

  • A thresher shark. 

How often have the words flail and thrasher occurred in a corpus of books? (source: Google Ngram Viewer )