spend a penny vs wet

spend a penny is not a noun while wet is a noun.

Word	Noun	Adjective	Verb	Adverb
spend a penny	No	No	Yes	No
wet	Yes	Yes	Yes	No

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

Other hyponyms of spend a penny include stale.

spend a penny (noun)	wet (noun)
	wetness caused by water

spend a penny (adjective)	wet (adjective)
	covered or soaked with a liquid such as water
	producing or secreting milk
	supporting or permitting the legal production and sale of alcoholic beverages
	containing moisture or volatile components
	consisting of or trading in alcoholic liquor
	very drunk

spend a penny (verb)	wet (verb)
eliminate urine	make one's bed or clothes wet by urinating
	cause to become wet