catchment vs tarn

catchment

noun
  • A catchment area, or the people it serves. 

  • Any structure or land feature which catches and holds water; the collection of such water. 

verb
  • To divide into catchment areas. 

tarn

noun
  • One of many small mountain lakes or ponds. 

  • A small mountain lake, especially in Northern England. 

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