fatigue vs overfatigue

fatigue is a noun but overfatigue is not a noun.

Word	Noun	Adjective	Verb	Adverb
fatigue	Yes	No	Yes	No
overfatigue	No	No	Yes	No

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

Other hyponyms of fatigue include beat, exhaust, tucker, tucker out, wash up, overtire, overweary.

fatigue (noun)	overfatigue (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)	overfatigue (verb)
exhaust or get tired through overuse or great strain or stress	tire excessively
lose interest or become bored with something or somebody