WordNet records no synonym and no antonym for common denominator. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
an integer that is a common multiple of the denominators of two or more fractions
an attribute that is common to all members of a category
Synonyms, antonyms and the broader and narrower relations for common denominator come from Princeton University’s WordNet. Full sources and licences.