believable vs gelastic

believable

adj
  • Capable of being believed; credible. 

gelastic

adj
  • Pertaining to laughter, used in laughing, or to be the subject of laughter. 

  • Relating to a particularly severe form of epileptic fit, in which there is a sudden burst of energy. 

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