observe vs observance

observe is not a noun while observance is a noun.

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

observe (noun)	observance (noun)
	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

observe (verb)	observance (verb)
stick to correctly or closely
make mention of
watch attentively
observe with care or pay close attention to
discover or determine the existence, presence, or fact of by perception with the eyes
follow with the eyes or the mind
show respect towards
behave as expected during of holidays or rites
conform one's action or practice to