WordNet records no synonym and no antonym for guru. 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 Hindu or Buddhist religious leader and spiritual teacher
each of the first ten leaders of the Sikh religion
a recognized leader in some field or of some movement
“a guru of genomics”
Synonyms, antonyms and the broader and narrower relations for guru come from Princeton University’s WordNet. Full sources and licences.