funday vs Sun

funday and Sun both are nouns.

Word	Noun	Adjective	Verb	Adverb
funday	Yes	No	No	No
Sun	Yes	No	No	No

As nouns, Sun is a hypernym of funday; that is, Sun is a word with a broader meaning than funday:

funday: Sunday as a day for relaxing and having fun
Sun: first day of the week; observed as a day of rest and worship by most Christians

Other hypernyms of funday include Dominicus, Lord's Day, Sunday.

funday (noun)	Sun (noun)
Sunday as a day for relaxing and having fun	the star that is the source of light and heat for the planets in the solar system
	first day of the week; observed as a day of rest and worship by most Christians