calculus vs calculate

calculus is a noun but calculate is not a noun.

Word	Noun	Adjective	Verb	Adverb
calculus	Yes	No	No	No
calculate	No	No	Yes	No

calculus (noun)	calculate (noun)
the branch of mathematics that is concerned with limits and with the differentiation and integration of functions
a hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body
an incrustation that forms on the teeth and gums

calculus (verb)	calculate (verb)
	make a mathematical calculation or computation
	specifically design a product, event, or activity for a certain public
	judge to be probable
	have faith or confidence in
	predict in advance
	keep an account of