bracken vs thicket

bracken

noun
  • An area of countryside heavily populated by this fern. 

  • Any of several coarse ferns, of the genus Pteridium, that form dense thickets; often poisonous to livestock. 

thicket

noun
  • A dense, but generally small, growth of shrubs, bushes or small trees; a copse. 

  • A dense aggregation of other things, concrete or abstract. 

  • The collection of many small linked files created when a document is saved in HTML format by some word processors and web site creation software. 

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