A defining vocabulary is a list of words used by lexicographers to write dictionary definitions.
When the Longman Dictionary of Contemporary English was first published in 1978, its most striking feature was its use of a 2,000-word defining vocabulary based on Michael West's General Service List, and since then defining vocabularies have become a standard component of monolingual learner's dictionaries for English and for other languages.
Using a defining vocabulary is not without its problems, and some scholars have argued that it can lead to definitions which are insufficiently precise or accurate, or that words in the list are sometimes used in non-central meanings.
[2] The more common view, however, is that the disadvantages are outweighed by the advantages,[3][4] and there is some empirical research which supports this position.
Intermediate-level language learners are likely to have receptive familiarity with most words in a typical 2,000-word defining vocabulary.