flail vs thresh

flail

verb
  • To beat using a flail or similar implement. 

  • To wave or swing vigorously 

  • To thresh. 

  • To move like a 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. 

thresh

verb
  • To beat soundly, usually with some tool such as a stick or whip; to drub. 

  • To violently toss the limbs about. 

  • To separate the grain from the straw or husks (chaff) by mechanical beating, with a flail or machinery. 

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