equivocation vs tergiversation

equivocation

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

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

tergiversation

noun
  • The act of evading any clear course of action or speech, of being deliberately ambiguous; equivocation; fickleness. 

  • The act of abandoning something or someone, of changing sides; desertion; betrayal. 

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