plunge vs sheathe

plunge is a noun but sheathe is not a noun.

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

As verbs, sheathe is a hyponym of plunge; that is, sheathe 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, submerge, submerse, soak.

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

plunge (verb)	sheathe (verb)
begin with vigor	enclose with a sheath
devote (oneself) fully to	cover with a protective sheathing
cause to be immersed	plunge or bury (a knife or sword) in flesh
immerse briefly into a liquid so as to wet, coat, or saturate
thrust or throw into
fall abruptly
drop steeply
dash violently or with great speed or impetuosity