pay vs spend

pay is a noun but spend is not a noun.

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

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

pay (noun)	spend (noun)
something that remunerates

pay (verb)	spend (verb)
dedicate	pay out
bear (a cost or penalty), in recompense for some action	spend completely
convey, as of a compliment, regards, attention, etc.; bestow	use up a period of time in a specific way
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