wedding vs observance

wedding and observance both are nouns.

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

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

Other hypernyms of wedding include ceremonial, ceremonial occasion, ceremony.

wedding (noun)	observance (noun)
the act of marrying; the nuptial ceremony	the act of observing; taking a patient look
the social event at which the ceremony of marriage is performed	conformity with law or custom or practice etc.
a party of people at a wedding	the act of noticing or paying attention
	a formal event performed on a special occasion