plunge vs commence

plunge is a noun but commence is not a noun.

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

As verbs, commence is a hypernym of plunge; that is, commence is a word with a broader meaning than plunge:

Other hypernyms of plunge include begin, get, get down, set about, set out, start, start out.

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

plunge (verb)	commence (verb)
begin with vigor	take the first step or steps in carrying out an action
devote (oneself) fully to	set in motion, cause to start
cause to be immersed	get off the ground
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