A lexicon is simply another name for a dictionary. Both “lexicon” and “dictionary” came into English from Latin and both of them mean essentially the same thing. “Dictionary” was native to Latin—“lexicon” came from the Greek into Latin before being imported into English. For various historical reasons, however, scholars typically refer to dictionaries of ancient languages such as Greek and Hebrew as lexicons rather than dictionaries. The word “dictionary” is often used in Biblical Studies to refer to what, in normal usage, most people would consider an encyclopedia.