bur vs slub

bur

noun
  • A rotary cutting implement having a selection of variously shaped heads. 

  • Any of several plants having such husks. 

  • A rough, prickly husk around the seeds or fruit of some plants. 

slub

noun
  • A small thickened portion or knot found on linen yarn, caused by defects. 

  • Fabric fiber produced by slubbing. 

verb
  • To draw and twist fibers in order to prepare them for spinning. 

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