Vocabulary

A vocabulary is a set of words known to a person or other entity, or that are part of a specific language.

The vocabulary of a person is defined either as the set of all words that are understood by that person or the set of all words likely to be used by that person when constructing new sentences. So "curse" is a regular part of the vocabulary of native English speakers but "imprecate" is not, even though the two words are synonyms. The richness of a person's vocabulary is popularly thought to be a reflection of intelligence or level of education. Accordingly, many standardised tests, such as the SAT, have questions that test vocabulary.

Increasing the size of one's vocabulary, also called vocabulary building, is generally considered to be an important part of both learning a language and improving one's skills in a language in which one is already proficient. Hence schoolchildren are often taught new words as a part of a particular unit or lesson. Similarly, many adults find vocabulary building to be a fun and educational activity, as evidenced in the popularity of "word-a-day" services such as mailing lists and desktop calendars.

The word "vocabulary" is also used figuratively for qualities or techniques distinctive to a particular style, especially an architectural style.

Capacity
Jean Aitchison gives the capacity of the vocabulary of college graduates with Bachelor of Education degrees as an estimate of at least 50,000, where a word is defined as a lexeme or dictionary entry, i.e., sing, sings, sang, sung count as one entry sing.

According to Robert Waring, a 5-year-old native English speaker knows about 4,000 to 5,000 word families. They would add roughly 1000 new word families every year to their vocabulary. A university graduate will have a vocabulary of around 20,000 word families, in which tolerate, tolerance, intolerable, and toleration are considered as one word family.

Access time
According to Jean Aitchison the time to recognise a word may be less than 200ms after onset; in many cases the word is already recognised before it has even ended. (Shadowing and lexical decision tasks were used to determine this number).