whodunit

[hoo-duhn-it]
Also especially British, who·dun·nit.

Origin of whodunit

1925–30; jocular formation from question Who done it?, for standard English Who did it?
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for whodunnit

whodunnit

whodunit

noun
  1. informal a novel, play, etc, concerned with a crime, usually murder
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for whodunnit

whodunit

n.

"murder mystery," 1930, U.S. slang, originally a semi-facetious formation from who done it?

Online Etymology Dictionary, © 2010 Douglas Harper