illustrate vs expound

illustrate and expound both are verbs.

Word	Noun	Adjective	Verb	Adverb
illustrate	No	No	Yes	No
expound	No	No	Yes	No

As verbs, expound is a hypernym of illustrate; that is, expound is a word with a broader meaning than illustrate:

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

Other hypernyms of illustrate include dilate, elaborate, enlarge, expand, expatiate, exposit, flesh out, lucubrate.

illustrate (verb)	expound (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
depict with an illustration	state
supply with illustrations