Millstone Mill"stone`, n. One of two circular stones used for grinding grain or other substance in a mill[1]. [1913 Webster]

No man shall take the nether or the upper millstone to pledge. --Deut. xxiv. 6. [1913 Webster]

Note: The cellular siliceous rock called buhrstone is usually employed for millstones; also, some kinds of lava, as that Niedermendig, or other firm rock with rough texture. The surface of a millstone has usually a series of radial grooves in which the powdered material collects. [1913 Webster]

{Millstone girt} (Geol.), a hard and coarse, gritty sandstone, dividing the Carboniferous from the Subcarboniferous strata. See {Farewell rock}, under {Farewell}, a., and Chart of {Geology}.

{To see into a millstone} or {To see through a millstone}, to see into or through a difficult matter. (Colloq.) [1913 Webster]

The Collaborative International Dictionary of English. 2000.