terribly vs unbelievingly

terribly

adv
  • Very; extremely. 

  • Very badly. 

  • So as to cause terror or awe. 

unbelievingly

adv
  • Synonym of incredibly 

  • In an unbelieving way. 

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