instance vs expatiate

instance is a noun but expatiate is not a noun.

Word	Noun	Adjective	Verb	Adverb
instance	Yes	No	Yes	No
expatiate	No	No	Yes	No

As verbs, expatiate is a hypernym of instance; that is, expatiate is a word with a broader meaning than instance:

instance: clarify by giving an example of
expatiate: add details, as to an account or idea; clarify the meaning of and discourse in a learned way, usually in writing

Other hypernyms of instance include dilate, elaborate, enlarge, expand, exposit, expound, flesh out, lucubrate.

instance (noun)	expatiate (noun)
an item of information that is typical of a class or group
an occurrence of something

instance (verb)	expatiate (verb)
clarify by giving an example of	add details, as to an account or idea; clarify the meaning of and discourse in a learned way, usually in writing