Grinding away at a sub

"Although you might be just as likely to hear a submarine sandwich in New England called a 'sub' as anywhere else, New England has an additional term: 'grinder.' No, not the dating/social networking app, but a New England word that either referred to the Italian-American slang term for a dock worker or the fact that it took a lot of chewing to eat the hard crust of the bread. It’s worth noting that some only use the term grinder for a hot sandwich — using sub for other large sandwiches — and some call them all grinders.

-- From The Daily Meal (thedailymeal.com)