crusade

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of the military expeditions undertaken by European Christians in the 11th, 12th, and 13th centuries to recover control of the Holy Land from the Muslims.
• noun A holy war undertaken with papal sanction.
• noun A concerted effort or vigorous movement for a cause or against an abuse.
• intransitive verb To engage in a crusade.

from The Century Dictionary.

• To engage in a crusade; support or oppose any cause with zeal.
• noun A military expedition under the banner of the cross; specifically, one of the medieval expeditions undertaken by the Christians of Europe for the recovery of the Holy Land from the Mohammedans.
• noun Any vigorous concerted action for the defense or advancement of an idea or a cause, or in opposition to a public evil: as, a temperance crusade; the crusade against slavery.
• noun Same as crusado.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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 Any enterprise undertaken with zeal and enthusiasm.
• noun A Portuguese coin. See Crusado.
• intransitive verb To engage in a crusade; to attack in a zealous or hot-headed manner.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of the military expedition undertaken by the Christians of Europe in the 11th to 13th centuries to reconquer the Levant from the Muslims.
• noun figuratively A grand concerted effort toward some purportedly worthy cause.
• verb To make a grand concerted effort toward some purportedly worthy cause.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• 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
• 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