Sludge \Sludge\, n. [CF. {Slush}.] 1. Mud; mire; soft mud; slush. --Mortimer. Tennyson. 2. Small floating pieces of ice, or masses of saturated snow. --Kane. 3. (Mining) See {Slime}, 4. {Sludge hole}, the hand-hole, or manhole, in a steam boiler, by means of which sediment can be removed.