WordNet records no synonym and no antonym for parkinson's law. 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.
C. Northcote Parkinson's cynical observation that work will expand so as to fill the time available for its completion
C. Northcote Parkinson's cynical observation that the number of subordinates in an organization will increase linearly regardless of the amount of work to be done
Synonyms, antonyms and the broader and narrower relations for parkinson's law come from Princeton University’s WordNet. Full sources and licences.