optimum vs optimise

optimum is a noun but optimise is not a noun.

Word	Noun	Adjective	Verb	Adverb
optimum	Yes	Yes	No	No
optimise	No	No	Yes	No

optimum (noun)	optimise (noun)
most favorable conditions or greatest degree or amount possible under given circumstances

optimum (adjective)	optimise (adjective)
most desirable possible under a restriction expressed or implied

optimum (verb)	optimise (verb)
	act as an optimist and take a sunny view of the world
	make optimal; get the most out of; use best
	modify to achieve maximum efficiency in storage capacity or time or cost