shift ground vs tergiversate

shift ground

tergiversate

verb
  • To evade, to equivocate using subterfuge; to obfuscate in a deliberate manner. 

  • To flee by turning one's back. 

  • To change sides or affiliation; to apostatize. 

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