A 
lexicon is a 
dictionary -- a list of words together with additional information. 
In 
Linguistics, a lexicon has a slightly more specialized definition, as it includes the 
Lexemes used to actualize words.  Lexemes are formed according to 
morpho-syntactic rules and express 
sememes[?]. 
A lexicon may also be the mental vocabulary in a speaker's mind. Furthermore an indivividual 'lexical knowledge' is a term used in academia to refer to an individual's vocabulary knowledge.
 
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