A lexicon is a collection of words used in a particular language. It can also refer to the study of words and their meaning. In linguistics, a lexicon is often thought of as the mental dictionary that speakers use to store and retrieve information about the words they know.
The word “lexicon” comes from the Greek word λεξικόν (lexikon), which means “wordbook” or “dictionary.” The Latin equivalent is vocabularium or vocabulum. The first known use of the word dates back to 1603, when it was used in a work called Lexicon Technicum by John Harris.
Today, we use the term lexicon to refer to both dictionaries and other collections of words, such as those found in literature or specialist areas like medicine or law.
See Information Technology and Alphabet