WordNet records no synonym and no antonym for visible speech. 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.
a phonetic alphabet invented by Melville Bell in the 19th century
spectrogram of speech; speech displayed spectrographically
Synonyms, antonyms and the broader and narrower relations for visible speech come from Princeton University’s WordNet. Full sources and licences.