mill·stone /ˈmɪlˌston/
 磨石;重擔,負擔
 Mill·stone n. One of two circular stones used for grinding grain or other substance in a mill1.
    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 a millstone or To see through a millstone, to see into or through a difficult matter. (Colloq.)
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 millstone
      n 1: (figurative) something that hinders or handicaps; "she was
           an albatross around his neck" [syn: albatross]
      2: any load that is difficult to carry
      3: one of a pair of heavy flat disk-shaped stones that are
         rotated against one another to grind the grain