circumstantially vs incidentally

circumstantially

adv
  • In respect to circumstances; not essentially; accidentally. 

  • in a circumstantial manner 

  • In every circumstance or particular; minutely. 

incidentally

adv
  • In an incidental manner; not of central or critical importance. 

  • By chance; in an unplanned way. 

  • Parenthetically, by the way. 

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