poorness has 8 distinct synonyms spread across 2 of its 4 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.
the state of having little or no money and few or no material possessions
less than adequate
“the relative poorness of New England farmland”
the quality of being meager
“an exiguity of cloth that would only allow of miniature capes”
the quality of being poorly made or maintained
“she was unrecognizable because of the poorness of the photography”
Synonyms, antonyms and the broader and narrower relations for poorness come from Princeton University’s WordNet. Full sources and licences.