\Grind"stone`\, n.
A flat, circular stone, revolving on an axle, for grinding or
sharpening tools, or shaping or smoothing objects.

{To} {hold, pat, or bring} {one's nose to the grindstone}, to
   oppress one; to keep one in a condition of servitude.

         They might be ashamed, for lack of courage, to
         suffer the Laced[ae]monians to hold their noses to
         the grindstone.                       --Sir T.
                                               North.