the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
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"
a diversion that occupies one's time and thoughts (usually pleasantly); "sailing is her favorite pastime"; "his main pastime is gambling"; "he counts reading among his interests"; "they criticized the boy for his limited pursuits"