1. A work of REFERENCE listing and explaining words: Henry G. Liddell & Robert Scott, Greek–English Lexicon (1843). A lexicon is usually a dictionary that deals either with a classical or scriptural language or a technical or facetious subject ( Jonathon Green, The Cynic's Lexicon: A Dictionary of Amoral Advice, 1984). It may also, however, be a word list ( Roland Hindmarsh, The Cambridge English Lexicon, 1980) or a thematic work of lexical reference ( Tom McArthur, The Longman Lexicon of Contemporary English, 1981).
2. A term in especially American LINGUISTICS for the VOCABULARY of a language or sub-language, consisting of its stock of LEXEMES.
lex·i·con / ˈleksiˌkän; -kən/ • n. (pl. -cons or -ca / -kə/ ) 1. the vocabulary of a person, language, or branch of knowledge: the size of the English lexicon. ∎ a dictionary, esp. of Greek, Hebrew, Syriac, or Arabic: a Greek–Latin lexicon. 2. Linguistics the complete set of meaningful units in a language.
So lexicographer, lexicography XVII.