A vocabulary is the tool used by your brain to form thoughts.
Those doing research into mind reading (Legitimate thought reading, not ESP) have found that our thoughts are very much word oriented. Individual words come from specific parts of our brains and follow specific pathways. Once those pathways are mapped, they can know what a person is thinking with a fair degree of accuracy.
In the science show I watched, they had a subject wired up with an EEG. A TV screen would show them photograph of something like a beach in Hawaii. In the next room words would come from a computer program that had mapped the subject’s brain. Words on the screen would be things like beach, sand, palm, hotel, mountain, tropical.