For me, a tractor is the type of thing a farmer or someone would use. My dad has a fifteen year old tractor he uses to pull trees to a place where we can cut them, and to plough our driveway in the winter. The snow gets pushed into piles next to the driveway, and when I was little, my brothers and I would dig little caves in them.
What most people call a tractor trailer, I call a big truck, (emphasis on big) because everyone at Southern Tier Express, where my uncle works, calls them that, and that's what they work with all the time.