Dictionary.com
definitions

Whitmonday

[hwit-muhn-dey, -dee, wit-]
noun
  1. the Monday following Whitsunday.

Origin of Whitmonday

First recorded in 1550–60; modeled on Whitsunday
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for whit monday

Whit Monday

noun
  1. the Monday following Whit Sunday
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