From French croisade, introduced into English (in the French spelling) by 1575. The modern spelling emerges c. 1760,. Middle French croisade is introduced in the 15th century, based on Spanish cruzada (late 14th century) and Old Occitan crozada (early 13th century), both reflecting Medieval Latin cruciāta, cruxiata, the feminine singular of the adjective cruciātus used as an abstract noun. Adjectival cruciātus originally meant "tormented; crucified", but from the 12th century crucesignatus was also used for "marked with a cross; making the sign of the cross" and eventually "taking the cross" in the sense of "going on a crusade". Old Occitan crozada is used in the sense "[the Albigensian] crusade" in the Song of the Albigensian crusade, written c. 1213. From vernacular usage, Middle Latin cruciāta also comes to be used in the sense "crusade" from about 1270.
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.1837, L[etitia] E[lizabeth] L[andon], “Arrived at Home”, in Ethel Churchill: Or, The Two Brides. […], volume I, London: Henry Colburn, […], →OCLC, page 87:
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.
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.1994, Richard Nixon, “America Beyond Peace”, in Beyond Peace, New York: Random House, →ISBN, →LCCN, →OCLC, page 239:
From French croisade, introduced into English (in the French spelling) by 1575. The modern spelling emerges c. 1760,. Middle French croisade is introduced in the 15th century, based on Spanish cruzada (late 14th century) and Old Occitan crozada (early 13th century), both reflecting Medieval Latin cruciāta, cruxiata, the feminine singular of the adjective cruciātus used as an abstract noun. Adjectival cruciātus originally meant "tormented; crucified", but from the 12th century crucesignatus was also used for "marked with a cross; making the sign of the cross" and eventually "taking the cross" in the sense of "going on a crusade". Old Occitan crozada is used in the sense "[the Albigensian] crusade" in the Song of the Albigensian crusade, written c. 1213. From vernacular usage, Middle Latin cruciāta also comes to be used in the sense "crusade" from about 1270.
1
To go on a military crusade.
2
To make a grand concerted effort toward some purportedly worthy cause.
He crusaded against similar injustices for the rest of his life.
Etymology Capitalised by Mills, The History of the Crusades (1820) when referring to a specific campaign ("The third and fourth Crusades" p. 95) but not when referring to the general concept ("the clergy successfully preached the crusade through all the German state" p. 87). More at crusade.
1
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.