declension vs plummeting

declension

noun
  • A falling off, decay or descent. 

  • A way of categorizing nouns, pronouns, or adjectives according to the inflections they receive. 

  • The product of that act; a list of declined forms. 

  • The act of declining a word; the act of listing the inflections of a noun, pronoun or adjective in order. 

plummeting

noun
  • A violent or dramatic fall. 

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