fatigue vs poop out

fatigue is a noun but poop out is not a noun.

Word	Noun	Adjective	Verb	Adverb
fatigue	Yes	No	Yes	No
poop out	No	No	Yes	No

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

Other hyponyms of fatigue include conk out, peter out, run down, run out, retire, withdraw.

fatigue (noun)	poop out (noun)
labor of a nonmilitary kind done by soldiers (cleaning or digging or draining or so on)
(always used with a modifier) boredom resulting from overexposure to something
temporary loss of strength and energy resulting from hard physical or mental work
used of materials (especially metals) in a weakened state caused by long stress

fatigue (verb)	poop out (verb)
exhaust or get tired through overuse or great strain or stress	use up all one's strength and energy and stop working
lose interest or become bored with something or somebody