What Makes Soup a Stew?

I knew I had a ton of vegetables in the fridge that needed to be used, so I had an idea this evening to make a pot of veggie stew.  I didn't have a recipe to work from (I usually don't enjoy following them anyway) so I started improvising.  I wanted a nice, savory broth with a little sweet, so after sauteeing eggplant, patty pan squash, yellow bell pepper, onion, wax beans, red potatoes, carrot and garlic, I added a bit of water and copious amounts of vegetable buillion paste.  It was very strong and salty, to the point I got nervous that I had added too much.  But once the veggies started to simmer on a very low heat, and I added tomatoes, the sweet began to blend quite nicely with the savory salty broth.  I accompanied the stew with some lovely raisin-pecan bread from Stone Circle Bakery.  At dinner, B inquired about the soup I was serving.  When I corrected her, saying it was actually a stew, she challenged me right back.  I tried to explain that a stew is like soup, but less...well, soupy!  That was a lame explanation even to my own ears so I didn't corrrect her when she referred to dinner as soup for the rest of the evening.