mutation vs severing

mutation

noun
  • Any alteration or change. 

  • An alteration a particular sound of a word, especially the initial consonant, which is triggered by the word's morphological or syntactic context and not by its phonological context. 

  • A group of thrushes. 

  • A mutant. 

  • Any heritable change of the base-pair sequence of genetic material. 

severing

noun
  • The act by which something is severed. 

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