solidity has 1 distinct synonym 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 2 recorded opposites are porosity, hollowness.
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 consistency of a solid
Synonyms, antonyms and the broader and narrower relations for solidity come from Princeton University’s WordNet. Full sources and licences.
state of having the interior filled with matter
the quality of being solid and reliable financially or factually or morally
“the solidity of the evidence worked in his favor”