Millstone
Pronunciation : Mill"stone`
Part of Speech : n.
Definition : Defn: One of two circular stones used for grinding grain or other substance. No man shall take the nether or the upper millstone to pledge. Deut. xxiv. 6.
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. 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, or through, a millstone, to see into or through a difficult matter. (Colloq.)
Source : Webster's Unabridged Dictionary, 1913