start out vs plunge

start out is not a noun while plunge is a noun.

Word	Noun	Adjective	Verb	Adverb
start out	No	No	Yes	No
plunge	Yes	No	Yes	No

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

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

start out (verb)	plunge (verb)
take the first step or steps in carrying out an action	begin with vigor
depart for someplace	devote (oneself) fully to
	cause to be immersed
	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