A Grinder

One who grinds something, such as the teeth. (one who sharpens scissors)
(anatomy) A molar.
(slang) Any tooth.
A power tool with a spinning abrasive disc, used for grinding, smoothing, and shaping materials, usually metal.
(US, regional, western New England) A sandwich made on a long, cylindrical roll.
A kitchen gadget for processing coffee, herbs etc. into small or powdered pieces
The restless flycatcher (*Myiagra inquieta*) of Australia, which makes a noise like a scissors grinder.
(music, slang) A fan or performer of grindcore music.
(slang) A biohacker who uses cybernetic implants or biochemicals to enhance or change their own body.
(slang, dated) A student who studies hard; a swot.
(slang, dated) A person who coaches students for an upcoming examination.
(ice hockey, slang) A hard-working, physical player with limited offensive ability.
(lawyer slang) A low-ranking attorney with no clients who works very hard.
(US, military, slang) An outdoor space for drills and parades.
(radio, informal) Atmospheric interference producing a roaring background noise.

The type of sandwich denoted by grinder varies widely. In the Philadelphia area, for example, a grinder is distinguished from a hoagie in that the grinder is toasted or baked, and usually lacks lettuce.