flail vs knout

flail

verb
  • To move like a flail. 

  • To beat using a flail or similar implement. 

  • To wave or swing vigorously 

  • To thresh. 

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. 

knout

verb
  • To flog or beat with a knout. 

noun
  • A leather scourge (multi-tail whip), in the severe version known as 'great knout' with metal weights on each tongue, notoriously used in imperial Russia. 

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