believably vs possibly

believably

adv
  • Used to express the speaker's assessment of the credibility of a reported statement. 

  • In a believable way. 

possibly

adv
  • Perhaps; indicates that the proposition may be true (is not certainly false) regardless of any facts or circumstances known to, stated by or implied by the speaker. 

  • In the realm of possibility; indicates that the action may successfully be performed (is not impossible) regardless of any facts or circumstances known to, stated by or implied by the speaker that might limit the performance. 

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