facetiously vs tongue-in-cheek

facetiously

adv
  • In a facetious or flippant manner; in a manner that treats serious issues with deliberately inappropriate humor 

tongue-in-cheek

adv
  • With irony. 

adj
  • Not intended seriously; jocular or humorous. 

How often have the words facetiously and tongue-in-cheek occurred in a corpus of books? (source: Google Ngram Viewer )