gag vs in-joke

gag

noun
  • A joke or other mischievous prank. 

  • Mycteroperca microlepis, a species of grouper. 

  • Any suppression of freedom of speech. 

  • An order or rule forbidding discussion of a case or subject. 

  • A device to restrain speech, such as a rag in the mouth secured with tape or a rubber ball threaded onto a cord or strap. 

  • a device or trick used to create a practical effect; a gimmick 

  • A convulsion of the upper digestive tract. 

verb
  • To restrain someone's speech by blocking his or her mouth. 

  • To cause to heave with nausea. 

  • To pry or hold open by means of a gag. 

  • To choke; to retch. 

  • To experience the vomiting reflex. 

  • To restrain someone's speech without using physical means. 

  • To astonish (someone); to be at a loss for words. 

in-joke

noun
  • Synonym of inside joke (“a joke that is understood or meant to be understood only by certain people who are aware of the details”) 

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