any of the more or less continuous military expeditions in the 11th to 13th centuries when Christian powers of Europe tried to recapture the Holy Land from the Muslims(noun.act)
source: wordnet30
Any one of the military expeditions undertaken by Christian powers, in the 11th, 12th, and 13th centuries, for the recovery of the Holy Land from the Mohammedans.(noun)
source: webster1913
verb (v)
exert oneself continuously, vigorously, or obtrusively to gain an end or engage in a crusade for a certain cause or person; be an advocate for(verb.social)