A Lexicon is similar to a Greek-other language dictionary, although it usually deals with the languages of the Scriptures, (Greek Aramaic Syrica and Hebrew) and the modern language, (English, Spanish, Modern Greek etc.) and not general topics.
Both Catholics and Protestants have written Lexicons. An example of some of the differences would be, Prebyteros would be translated in a Catholic Lexicon as meaning Elder and priest. Most Protestant Lexicons will leave out priest because they don’t accept that the priests in the Early Church existed and were invented by the Catholic Church at a later date.