observance vs ceremonial

observance and ceremonial both are nouns.

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

As nouns, observance and ceremonial are synonyms defined as:

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

Other synonyms of observance include ceremonial occasion, ceremony.

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

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