maintain vs preserve

maintain is not a noun while preserve is a noun.

Word	Noun	Adjective	Verb	Adverb
maintain	No	No	Yes	No
preserve	Yes	No	Yes	No

As verbs, maintain and preserve are synonyms defined as:

maintain and preserve: keep in safety and protect from harm, decay, loss, or destruction

Other synonyms of maintain include conserve, keep up.

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

maintain (noun)	preserve (noun)
	fruit preserved by cooking with sugar
	a reservation where animals are protected
	a domain that seems to be specially reserved for someone

maintain (verb)	preserve (verb)
stick to correctly or closely	prevent (food) from rotting
state categorically	keep in safety and protect from harm, decay, loss, or destruction
state or assert	to keep up and reserve for personal or special use
support against an opponent	keep or maintain in unaltered condition; cause to remain or last
maintain by writing regular records	maintain in safety from injury, harm, or danger
supply with necessities and support	keep undisturbed for personal or private use for hunting, shooting, or fishing
keep in safety and protect from harm, decay, loss, or destruction
have and exercise
maintain for use and service
cause to continue in a certain state, position, or activity