incredibly vs unconceivably

incredibly

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

  • In an incredible manner; not to be believed. 

  • To a great extent; extremely. 

unconceivably

adv
  • Synonym of inconceivably 

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