Lord's Day vs funday

Lord's Day and funday both are nouns.

Word	Noun	Adjective	Verb	Adverb
Lord's Day	Yes	No	No	No
funday	Yes	No	No	No

As nouns, funday is a hyponym of Lord's Day; that is, funday is a word with a more specific, narrower meaning than Lord's Day:

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

Lord's Day (noun)	funday (noun)
first day of the week; observed as a day of rest and worship by most Christians	Sunday as a day for relaxing and having fun