observance vs ceremony

observance and ceremony both are nouns.

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

As nouns, observance and ceremony are synonyms defined as:

Other synonyms of observance include ceremonial, ceremonial occasion.

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