Definition of "lexicon"

The vocabulary of a language.  examples

(lexicography, linguistics) A dictionary that includes or focuses on lexemes.  examples

A dictionary of Classical Greek, Hebrew, Latin, or Aramaic.  examples

(programming) The lexicology of a programming language. (Usually called lexical structure.)  examples

(rare) Any dictionary.

The vocabulary used by or known to an individual. (Also called lexical knowledge.)  examples

A set of vocabulary specific to a certain subject.

1. A list thereof.  examples