O.E.
grindan, forgrindan "destroy by crushing" (class III strong verb; past tense
grand, pp.
grunden), from P.Gmc.
*grindanan (cf. Du.
grenden), related to
ground, from PIE
*ghrendh- "crushing" (cf. L.
frendere "to gnash the teeth," Gk.
khondros "corn, grain," Lith.
grendu "to scrape, scratch"). The noun sense "steady, hard work" first recorded 1851 in college student slang; the meaning "hard-working student" is Amer.Eng. slang from 1864.
Grinder as a type of large sandwich is first recorded 1954. To
keep one's nose to the grindstone was originally to get control of another and treat him harshly:
"This Text holdeth their noses so hard to the grindstone, that it clean disfigureth their Faces." [Frith, "Mirror to know Thyself," 1532]
The main modern (reflective) sense of "work hard" is from 1828.