pancake day vs Shrove Tuesday

pancake day and Shrove Tuesday both are nouns.

Word	Noun	Adjective	Verb	Adverb
pancake day	Yes	No	No	No
Shrove Tuesday	Yes	No	No	No

As nouns, pancake day and Shrove Tuesday are synonyms defined as:

Other synonyms of pancake day include Fat Tuesday, Mardi Gras.

pancake day (noun)	Shrove Tuesday (noun)
the last day before Lent	the last day before Lent