WordNet records no synonym and no antonym for dockyard. It is the only member of its synset, 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.
an establishment on the waterfront where vessels are built or fitted out or repaired
Synonyms, antonyms and the broader and narrower relations for dockyard come from Princeton University’s WordNet. Full sources and licences.