Hoagies. Grinders. Subs. Cursory online research will tell you that each of these names has a distinct origin, with "hoagie" referring to a type of sandwich that was popular among Italian workers on Hog Island in Pennsylvania (get it?); "grinder" a slang term for dockworkers who were fans of a similarly structured sandwich; and the "sub" being a broad descriptor for any long, spherical sandwich that resembles a submarine.
Okay, I buy that different nomenclature emerged for what is essentially the same sandwich: a longish roll filled with meats, some roughage (lettuce, tomato, onions, etc.), dressings and perhaps some cheese. Regional dialects certainly give rise to multiple referents for one object (see the famous woodlouse example).
But at least from my own experience, I think there are nuances that distinguish these three sandwiches, or at least perpetuate the existence of different names. Let's take a look:
Hoagie: More strongly associated with Italian-American culture, and in my observation used only to refer to sandwiches containing cold cuts such as ham, salami, turkey, etc. Also, when people use the term "hoagie," they most often seem to be referring to a sandwich that is at least 12 inches in length, if not longer (aka, the "party hoagie").
Grinder: I have never ever heard anyone south of the Mason-Dixon Line mention a "grinder" unless the word "nutmeg" immediately preceded it. Okay, well, that's an exaggeration, but I seriously cannot recall the last time I heard that word in Texas. The only time, in fact, I regularly encounter "grinder" is in New York and New Jersey, where it's used more often to describe a spherical sandwich that is toasted and/or contains hot ingredients such as meatballs, sliced chicken, etc.
Sub: "Sub" is pretty much ubiquitous nationwide (thanks, perhaps, to Subway), though it seems the vaguest of the three terms. There are hot subs and cold subs, subs with cold cuts (turkey), subs with hot meats (chicken parmesan), subs that are short, subs that are long.
Some of you may also wonder why the po-boy and the gyro (hero) are not included in this meditation on sandwiches. The short answer is that I see both as more readily distinguished by their distinctive components and less tenuous links to different ethnic groups.
So, perhaps all grinders are subs but not all subs are grinders? Are hoagies and subs basically interchangeable? Readers, please weigh in on what if anything differentiates these sandwiches and how you use these terms.