roundness has 3 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. Its one recorded opposite is angularity.
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 quality of being round numbers
“he gave us the results in round numbers, but their roundness didn't affect the point he was making”
Synonyms, antonyms and the broader and narrower relations for roundness come from Princeton University’s WordNet. Full sources and licences.
the property possessed by a line or surface that is curved and not angular
the bodily property of being well rounded