Or, as I ponder phrasing it another way, if you were to say "Bean, you may not use the word semi-trailer to refer to the entire truck, for that is technically incorrect" I would be at a loss for another word to fill that linguistic hole in my idiolect. Everyone I know calls the whole kit-and-caboodle a semi-trailer. I would get a blank stare for articulated lorry and a very delayed reaction for tractor trailer.