grind (v.) Look up grind at Dictionary.com
Old English grindan "to rub together, grate, scrape," forgrindan "destroy by crushing" (class III strong verb; past tense grand, past participle grunden), from Proto-Germanic *grindanan (cognates: Dutch grenden), related to ground, from PIE *ghrendh- "to grind" (cognates: Latin frendere "to gnash the teeth," Greek khondros "corn, grain," Lithuanian grendu "to scrape, scratch"). Meaning "to make smooth or sharp by friction" is from c.1300. Most other Germanic languages use a verb cognate with Latin molere (compare Dutch malen, Old Norse mala, German mahlen).
grind (n.) Look up grind at Dictionary.com
late 12c., "gnashing the teeth," from grind (v.). The sense "steady, hard work" first recorded 1851 in college student slang (but compare gerund-grinder, 1710); the meaning "hard-working student" is American English slang from 1864.