attending vs observance

attending and observance both are nouns.

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

As nouns, observance is a hyponym of attending; that is, observance is a word with a more specific, narrower meaning than attending:

attending: the process whereby a person concentrates on some features of the environment to the (relative) exclusion of others
observance: the act of noticing or paying attention

Other hyponyms of attending include attentiveness, heed, paying attention, regard, clock-watching, ear, eye, notice, observation, notice.

attending (noun)	observance (noun)
the act of being present (at a meeting or event etc.)	the act of observing; taking a patient look
the process whereby a person concentrates on some features of the environment to the (relative) exclusion of others	conformity with law or custom or practice etc.
	the act of noticing or paying attention
	a formal event performed on a special occasion

attending (adjective)	observance (adjective)
giving practical help to