Vocabulary (noun)

1. The set of words used by or known to a particular person or group of people.
2. The body of words used in a particular language or subject.

Origin:

From the latin word "vocabularius" meaning "of or belonging to words".

Examples:

1. He had a vast vocabulary and could use words precisely.
2. She was trying to expand her vocabulary by reading more books.
3. The vocabulary of the novel was quite challenging for the young reader.
4. The vocabulary of the field of medicine is quite extensive and specialized.
5. The vocabulary of the language was quite different from what she was used to.