The Origin of Hoagies, Grinders, Subs, Heroes, and ...
grind (n.) 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.