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 ]
☞ 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.),
To see into a millstone
To see through a millstone