billow vs expand

billow is a noun but expand is not a noun.

Word	Noun	Adjective	Verb	Adverb
billow	Yes	No	Yes	No
expand	No	No	Yes	No

As verbs, expand is a hypernym of billow; that is, expand is a word with a broader meaning than billow:

billow (noun)	expand (noun)
a large sea wave

billow (verb)	expand (verb)
become inflated	grow vigorously
rise and move, as in waves or billows	exaggerate or make bigger
rise up as if in waves	become larger in size or volume or quantity
move with great difficulty	expand the influence of
	make bigger or wider in size, volume, or quantity
	add details, as to an account or idea; clarify the meaning of and discourse in a learned way, usually in writing
	extend in one or more directions