fatigue has 15 distinct synonyms spread across 4 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
temporary loss of strength and energy resulting from hard physical or mental work
“he was hospitalized for extreme fatigue”
used of materials (especially metals) in a weakened state caused by long stress
“metal fatigue”
(always used with a modifier) boredom resulting from overexposure to something
“he was suffering from museum fatigue”
labor of a nonmilitary kind done by soldiers (cleaning or digging or draining or so on)
“the soldiers were put on fatigue to teach them a lesson”
Synonyms, antonyms and the broader and narrower relations for fatigue come from Princeton University’s WordNet. Full sources and licences.