Mahdism \Mah"dism\, n. Belief in the coming of the Mahdi; fanatical devotion to the cause of the Mahdi or a pretender to that title. -- {Mah"dist}, n. Mahdism has proved the most shameful and terrible instrument of bloodshed and oppression which the modern world has ever witnessed. --E. N. Bennett. [Webster 1913 Suppl.]