WordNet records no synonym and no antonym for seventh crusade. 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.
a Crusade initiated in 1248 after the loss of Jerusalem in 1244 and defeated in 1249
Synonyms, antonyms and the broader and narrower relations for seventh crusade come from Princeton University’s WordNet. Full sources and licences.