grind (v.) Look up grind at Dictionary.com
Old English grindan "to rub together, crush into powder, 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 Old English, "the gnashing of teeth;" c. 1200, "the act of chewing or grinding," from grind (v.). The sense "steady, hard, tedious work" first recorded 1851 in college student slang (but compare gerund-grinder, 1710); the meaning "hard-working student, one who studies with dogged application" is American English slang from 1864. Slang meaning "sexual intercourse" is by 1893.