ceremonial vs observance

ceremonial and observance both are nouns.

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

As nouns, ceremonial and observance are synonyms defined as:

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

Other synonyms of ceremonial include ceremonial occasion, ceremony.

ceremonial (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

ceremonial (adjective)	observance (adjective)
marked by pomp or ceremony or formality