Whitsun Monday vs Whitmonday

Whitsun Monday and Whitmonday both are nouns.

Word	Noun	Adjective	Verb	Adverb
Whitsun Monday	Yes	No	No	No
Whitmonday	Yes	No	No	No

As nouns, Whitsun Monday and Whitmonday are synonyms defined as:

Whitsun Monday and Whitmonday: the day after Whitsunday; a legal holiday in England and Wales and Ireland

Whitsun Monday (noun)	Whitmonday (noun)
the day after Whitsunday; a legal holiday in England and Wales and Ireland	the day after Whitsunday; a legal holiday in England and Wales and Ireland