k vs cardinal

k and cardinal both are nouns.

Word	Noun	Adjective	Verb	Adverb
k	Yes	Yes	No	No
cardinal	Yes	Yes	No	No

k (noun)	cardinal (noun)
the 11th letter of the Roman alphabet	crested thick-billed North American finch having bright red plumage in the male
	a variable color averaging a vivid red
	(Roman Catholic Church) one of a group of more than 100 prominent bishops in the Sacred College who advise the Pope and elect new Popes
	the number of elements in a mathematical set; denotes a quantity but not the order

k (adjective)	cardinal (adjective)
denoting a quantity consisting of 1,000 items or units	being or denoting a numerical quantity but not order
	serving as an essential component