invigorate vs overburden

invigorate

verb
  • To impart vigor, strength, or vitality to. 

  • To heighten or intensify. 

  • To make lively. 

  • To give life or energy to. 

overburden

verb
  • To overload or overtax. 

noun
  • A sterile stratum that lies above the stratum being investigated 

  • The rock and subsoil that lies above a mineral deposit such as a coal seam. 

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