Definition of "Crusade" :

noun: a series of actions advancing a principle or tending toward a particular end

noun: 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

verb: go on a crusade; fight a holy war

verb: 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