WordNet records no synonym and no antonym for yeomanry. 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.
class of small freeholders who cultivated their own land
a British volunteer cavalry force organized in 1761 for home defense later incorporated into the Territorial Army
Synonyms, antonyms and the broader and narrower relations for yeomanry come from Princeton University’s WordNet. Full sources and licences.