incredibly vs terribly

incredibly

adv
  • To a great extent; extremely. 

  • In an incredible manner; not to be believed. 

  • Used to note the surprising or hard-to-believe nature of what is being said and suggest that it is nevertheless true. 

terribly

adv
  • Very; extremely. 

  • Very badly. 

  • So as to cause terror or awe. 

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