A vocabulary is a list of words.
The vocabulary a person uses is all the words that person knows and uses. In general, a person who is five knows about 4,000 to 5,000 words. Adults who have gone to college may know 20,000 words. A hearing vocabulary and reading vocabulary are bigger than a speaking vocabulary or writing vocabulary, as people understand some words that they do not use.
The number of words in a language is more than the words listed in one dictionary. One dictionary may have a list of 500,000 (half a million) words. Another dictionary may have some other words that the other dictionary does not have. Adding up all the words in those dictionaries, there are about 750,000 words in English. There may be more words than that.
The vocabulary of a language is always changing. New words are made or words change their meaning. Words about computers, like "download" are new to the English language. The new word "bling" came from hip hop. Words like "cool" have developed new meanings.
- Nation, Paul, and Robert Waring. 1997. Vocabulary size, text coverage and word lists. Vocabulary: Description, acquisition and pedagogy, 6-19. 
- Goulden R; Nation P. & Read J. 1990. How large can a receptive vocabulary be? Applied Linguistics 11: 341-363.
- Crystal, David 1995. The Cambridge encyclopedia of the English language. Cambridge University Press, p119, p423.
- Zipf G.K. 1949. Human behavior and the principle of least effort. Cambridge, Massachusetts: Addison-Wesley.
|Wikimedia Commons has media related to Vocabulary.|