equivocation vs vacillation

equivocation

noun
  • The use of expressions susceptible of a double signification, possibly intentionally and with the aim of misleading. 

  • A logical fallacy resulting from the use of multiple meanings of a single expression. 

vacillation

noun
  • Indecision in speech or action. 

  • Changing location by moving back and forth. 

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