plunge vs submerge

plunge is a noun but submerge is not a noun.

Word	Noun	Adjective	Verb	Adverb
plunge	Yes	No	Yes	No
submerge	No	No	Yes	No

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

Other hyponyms of plunge include dip, dunk, dip, douse, dunk, plunge, souse, dip, dip, submerse, soak, sheathe.

plunge (noun)	submerge (noun)
a brief swim in water
a steep and rapid fall

plunge (verb)	submerge (verb)
begin with vigor	fill or cover completely, usually with water
devote (oneself) fully to	cover completely or make imperceptible
cause to be immersed	put under water
immerse briefly into a liquid so as to wet, coat, or saturate	sink below the surface; go under or as if under water
thrust or throw into
fall abruptly
drop steeply
dash violently or with great speed or impetuosity