Grinder

wiktionary

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From Middle English grinder, grindere, from Old English grindere(“one or that which grinds; grinder”), equivalent to grind +‎ -er.

This etymology is incomplete. You can help Wiktionary by elaborating on the origins of this term.

etymonline

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grinder (n.)

Old English grindere "one who grinds (grain);" agent noun from grind (v.). Meaning "molar tooth" is late 14c. (Old English had grindetoð). Meaning "machine for milling" is from 1660s; of persons, from late 15c. "Large sandwich" sense is from 1954, American English, though the exact signification is uncertain (perhaps from the amount of chewing required to eat one).