observance vs social occasion

observance and social occasion both are nouns.

Word	Noun	Adjective	Verb	Adverb
observance	Yes	No	No	No
social occasion	Yes	No	No	No

As nouns, social occasion is a hypernym of observance; that is, social occasion is a word with a broader meaning than observance:

observance: a formal event performed on a special occasion
social occasion: a formal or official social gathering or ceremony of people

Other hypernyms of observance include affair, function, occasion, social affair, social function, social gathering.

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