superhuman vs unbelievable

superhuman

adj
  • Beyond what is possible for a human being. 

noun
  • A human being with remarkable abilities or superpowers. 

unbelievable

adj
  • Implausible or improbable. 

  • Not to be believed. 

  • Amazing, incredible; so surprising it is almost unable to believe. 

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