Webster’s Revised Unabridged Dictionary · 1913
Grindstone
Grind′stone′ (grīnd′stōn′), 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 Lacedæmonians to hold their noses to the grindstone. Sir T. North.