Corpsing is British theatrical slang for unintentionally laughing during a non-humorous performance or when a role in a humorous performance is intended to be played "straight". In North American TV and film, this is considered a variation of breaking character or simply "breaking".
The term appeared as "I should have been corpsed without a prompter." in 1840 in the book "Playing about: Or Theatrical Anecdotes and Adventures".  In 1853 Charles Dickens' Household Words provided this definition: "If an actor forgets his part while on the stage, he is said to "stick" and to "corpse" the actors who may be performing with him, by putting them out in their parts."  (in a theatrical context the term "out" meant "at a loss")
- arts.guardian.co.uk: "A greasepaint glossary," article on theatrical terms
- Hill, Benson Earle (1840). "Playing About; or, Theatrical Anecdotes and Adventures By Benson Earle Hill".
- Dickens, Charles (1853). "Household Words :, Volumes 7-8 edited by Charles Dickens".
- Johnson, Samuel; Perry, William (1805). "The Synonymous, Etymological, and Pronouncing English Dictionary".