richness has 12 distinct synonyms spread across 5 of its 7 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 property of being extremely abundant
“the profusion of detail”
the property of a sensation that is rich and pleasing
“the music had a fullness that echoed through the hall”
the quality of having high intrinsic value
“the richness of the mines and pastureland”
the property of producing abundantly and sustaining vigorous and luxuriant growth
“he praised the richness of the soil”
a strong deep vividness of hue
“the fire-light gave a richness of coloring to that side of the room”
splendid or imposing in size or appearance
“the grandness of the architecture”
Synonyms, antonyms and the broader and narrower relations for richness come from Princeton University’s WordNet. Full sources and licences.