howler vs in-joke

howler

noun
  • A hilarious joke. 

  • A tremendous lie; a whopper. 

  • A painfully obvious mistake. 

  • A bitterly cold day. 

  • A person hired to howl at a funeral. 

  • A serious accident (especially to come a howler or go a howler; compare come a cropper). 

  • That which howls, especially an animal such as a wolf or a howler monkey. 

  • A heavy fall. 

  • A 32-ounce ceramic, plastic, or stainless steel jug used to transport draft beer. 

  • A person who expresses aggression openly in the form of threats. 

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 howler and in-joke occurred in a corpus of books? (source: Google Ngram Viewer )