pay vs expend

pay is a noun but expend is not a noun.

Word	Noun	Adjective	Verb	Adverb
pay	Yes	No	Yes	No
expend	No	No	Yes	No

As verbs, expend is a hyponym of pay; that is, expend is a word with a more specific, narrower meaning than pay:

pay (noun)	expend (noun)
something that remunerates

pay (verb)	expend (verb)
dedicate	use up (resources or materials)
bear (a cost or penalty), in recompense for some action	pay out
convey, as of a compliment, regards, attention, etc.; bestow
give money, usually in exchange for goods or services
bring in
do or give something to somebody in return
cancel or discharge a debt
make a compensation for
discharge or settle
render
be worth it