Every speaker carries a mental stock of words. The lexicon is the complete inventory of words and fixed expressions in a language, or the subset known to an individual speaker.

Linguists model the lexicon as more than a list: entries include phonological form, grammatical properties, meaning, and collocation patterns. New words enter through coining, borrowing, and derivation; obsolete words drop out of active use. Specialized domains keep technical sublexicons.

Dictionaries attempt to describe the shared lexicon of a community at a given time. Psycholinguists study how lexical items are stored and retrieved. The size and structure of the lexicon shape what a language can express economically.

• Inventory of words and fixed expressions
• Described for languages and for individual speakers
• Includes form, meaning, and grammatical information
• Changes through innovation, borrowing, and loss