WordNet records no synonym and no antonym for instantiate. 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.
represent by an instance
“This word instantiates the usage that the linguists claimed to be typical for a certain dialect”
find an instance of (a word or particular usage of a word)
“The linguists could not instantiate this sense of the noun that he claimed existed in a certain dialect”
Synonyms, antonyms and the broader and narrower relations for instantiate come from Princeton University’s WordNet. Full sources and licences.