(1):

(n.) Any enterprise undertaken with zeal and enthusiasm; as, a crusade against intemperance.

(2):

(n.) A Portuguese coin. See Crusado.

(3):

(n.) 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.

(4):

(v. i.) To engage in a crusade; to attack in a zealous or hot-headed manner.