ceremony vs observance

ceremony and observance both are nouns.

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

As nouns, ceremony and observance are synonyms defined as:

Other synonyms of ceremony include ceremonial, ceremonial occasion.

ceremony (noun)	observance (noun)
the proper or conventional behavior on some solemn occasion	the act of observing; taking a patient look
any activity that is performed in an especially solemn elaborate or formal way	conformity with law or custom or practice etc.
a formal event performed on a special occasion	the act of noticing or paying attention
	a formal event performed on a special occasion