plant is a noun but monocotyledonous is not a noun.

plant is not an adjective while monocotyledonous is an adjective.

plant is a verb but monocotyledonous is not a verb.

plant (noun)	monocotyledonous (noun)
buildings for carrying on industrial labor
(botany) a living organism lacking the power of locomotion
an actor situated in the audience whose acting is rehearsed but seems spontaneous to the audience
something planted secretly for discovery by another

plant (adjective)	monocotyledonous (adjective)
	(of a flowering plant) having a single cotyledon in the seed as in grasses and lilies

plant (verb)	monocotyledonous (verb)
put or set (seeds, seedlings, or plants) into the ground
fix or set securely or deeply
set up or lay the groundwork for
place into a river
place something or someone in a certain position in order to secretly observe or deceive
put firmly in the mind