crusade

noun

1. (historical)Any of the Papally-endorsed military expeditions undertaken by the Christians of Latin Europe in the 11th to 13th centuries to reconquer the Levant from the Muslims, as well as expeditions along the Baltic Sea and against the Cathars.

   “During the crusades, many Muslims and Christians and Jews were slaughtered.”

   “Their way lay through the hall, where hung the helm of many a bold forefather, and arms that had seen service even in the crusades.”

2. Any war instigated and blessed by the Church for alleged religious ends, (especially) papal-sanctioned military campaigns against infidels or heretics.
3. (figuratively)A grand, concerted effort towards some purportedly worthy cause.

   “a crusade against drug abuse”

4. (dated)A mass gathering in a political campaign or during a religious revival effort.

   “The same period that has seen social and political crusades increasingly replace religious messages in the pulpits has seen a sharp 35 percent decline in membership of the mainline Protestant denominations associated with the National Council of Churches.”

5. (archaic)A Portuguese coin; a crusado.
6. (countable)Any of a series of religious campaigns by Christian forces from the 11th to the 13th century, mostly to capture the Holy Land from the Muslims and Jews who inhabited it.

verb

1. (intransitive)To go on a military crusade.
2. (intransitive)To make a grand concerted effort toward some purportedly worthy cause.

   “He crusaded against similar injustices for the rest of his life.”