• noun:   any of the more or less continuous military expeditions in the 11-13th centuries when Christian powers of Europe tried to recapture the Holy Land from the Muslims
• noun:   a series of actions advancing a principle or tending toward a particular end
• 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
• verb:   go on a crusade; fight a holy war

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