The word grind has several meanings:

1. To crush something into tiny pieces or powder by rubbing or pressing it. When you grind coffee beans, you break them down into fine particles that can brew into coffee. A pepper grinder crushes peppercorns into specks of pepper. Ancient civilizations used millstones to grind wheat into flour, and some people still use a mortar and pestle to grind spices by hand.
2. To rub or scrape something harshly against a surface. You might grind your teeth at night while sleeping, wearing them down without realizing it. Ice skates grind against the ice. Gears grind together if they're not working smoothly.
3. To work hard at something repetitive and sometimes tedious. Students sometimes talk about the grind of homework, studying, and practice. Athletes endure the grind of daily training. When you grind away at something, you keep working steadily even when it feels boring or exhausting. The daily grind refers to repetitive work or routines that can feel monotonous. This kind of grinding requires persistence: you show up and do the work, even when progress feels slow.