No, not SIN TAX; that’s an entirely different matter. I’m sure you hear the word “syntax” used (perhaps not as frequently as the homonym), but you might not be certain of its meaning.
SYNTAX means the way words are put together to form grammatical, comprehensible sentences. People who garble their meanings are said to speak and write using deficient syntax. Think of Sarah Palin and George W. Bush—they aren’t guilty all the time but often enough to be notorious for their use of the English language. The derivation of “syntax” is from Greek to Latin to French.
LEXICON refers to the vocabulary used by a person, by a language or by a branch of study, e.g., the lexicon of the Basque people of Catalonia. The derivation of “lexicon” is from Greek to Latin.