WordNet records no synonym and no antonym for vagueness. 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.
unclearness by virtue of being poorly expressed or not coherent in meaning
“the Conservative manifesto is a model of vagueness”
indistinctness of shape or character
“the scene had the swirling vagueness of a painting by Turner”
Synonyms, antonyms and the broader and narrower relations for vagueness come from Princeton University’s WordNet. Full sources and licences.