A lexicon, word-hoard, wordbook, or word-stock is the vocabulary of a person, language, or branch of knowledge (such as nautical or medical). In linguistics, a lexicon is a language’s inventory of lexemes. The word lexicon derives from the Greek λεξικόν (lexikon), neuter of λεξικός (lexikos) meaning ‘of or for words’.
Linguistic theories generally regard human languages as consisting of two parts: a lexicon, essentially a catalogue of a language’s words (its wordstock); and a grammar, a system of rules which allow for the combination of those words into meaningful sentences. The lexicon is also thought to include bound morphemes, which cannot stand alone as words (such as most affixes). In some analyses, compound words and certain classes of idiomatic expressions and other collocations are also considered to be part of the lexicon.
Dictionaries represent attempts at listing, in alphabetical order, the lexicon of a given language; usually, however, bound morphemes are not included.
The term “lexicon” is generally used in the context of single language. Therefore, multi-lingual speakers are generally thought to have multiple lexicons. Speakers of language variants (Brazilian Portuguese and European Portuguese, for example) may be considered to possess a single lexicon.
Thus a cash dispenser (British English) as well as an automatic teller machine or ATM in American English would be understood by both American and British speakers, despite each group using different dialects.
When linguists study a lexicon, they consider such things as what constitutes a word; the word/concept relationship; lexical access and lexical access failure; how a word’s phonology, syntax, and meaning intersect; the morphology-word relationship; vocabulary structure within a given language; language use (pragmatics); language acquisition; the history and evolution of words (etymology); and the relationships between words, often studied within philosophy of language.