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
go on a crusade; fight a holy war
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; "The liberal party pushed for reforms"; "She is crusading for women's rights"; "The Dean is pushing for his favorite candidate"
make an addition (to); join or combine or unite with others; increase the quality, quantity, size or scope of; "We added two students to that dorm room"; "She added a personal note to her letter"; "Add insult to injury"; "Add some extra plates to the dinner table"
make an addition by combining numbers; "Add 27 and 49, please!"
state or say further; "`It doesn't matter,' he supplied"
constitute an addition; "This paper will add to her reputation"