ceremonial occasion vs observance

ceremonial occasion and observance both are nouns.

Word	Noun	Adjective	Verb	Adverb
ceremonial occasion	Yes	No	No	No
observance	Yes	No	No	No

As nouns, ceremonial occasion and observance are synonyms defined as:

ceremonial occasion and observance: a formal event performed on a special occasion

Other synonyms of ceremonial occasion include ceremonial, ceremony.

ceremonial occasion (noun)	observance (noun)
a formal event performed on a special occasion	the act of observing; taking a patient look
	conformity with law or custom or practice etc.
	the act of noticing or paying attention
	a formal event performed on a special occasion