WordNet records no synonym and no antonym for second 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 from 1145 to 1147 that failed because of internal disagreements among the crusaders and led to the loss of Jerusalem in 1187
Synonyms, antonyms and the broader and narrower relations for second crusade come from Princeton University’s WordNet. Full sources and licences.