eccentricity has no recorded synonym. 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 concentricity.
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.
strange and unconventional behavior
(geometry) a ratio describing the shape of a conic section; the ratio of the distance between the foci to the length of the major axis
“a circle is an ellipse with zero eccentricity”
Synonyms, antonyms and the broader and narrower relations for eccentricity come from Princeton University’s WordNet. Full sources and licences.
a circularity that has a different center or deviates from a circular path