plant vs disposal plant

plant and disposal plant both are nouns.

As nouns, disposal plant is a hyponym of plant; that is, disposal plant is a word with a more specific, narrower meaning than plant:

plant (noun)	disposal plant (noun)
buildings for carrying on industrial labor	a plant for disposing of sewage
(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 (verb)	disposal plant (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