WordNet records no synonym and no antonym for burgrave. 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 nobleman ruling a German castle and surrounding grounds by hereditary right
the military governor of a German town in the 12th and 13th centuries
Synonyms, antonyms and the broader and narrower relations for burgrave come from Princeton University’s WordNet. Full sources and licences.