unfitness has 2 distinct synonyms spread across 2 of its 3 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. Its one recorded opposite is fitness.
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.
poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)
Synonyms, antonyms and the broader and narrower relations for unfitness come from Princeton University’s WordNet. Full sources and licences.
the quality of not being suitable
“the judges agreed on his unfitness for the appointment”