There was recent discussion on the B-Greek (Biblical-Greek) email list about creating a Koine-Koine lexicon. An ancient Greek-Greek lexicon does not currently exist. If you know English, both the Woodhouse Greek-English lexicon and the Louw-Nida Lexicon of Semantic Domains can help in finding Greek synonyms and parallel constructions. The Suda is more of an encyclopedia than a lexicon.
Very interesting! It’s organized by Latin headwords in alphabetical order, and it gives you all the Greek synonyms for a given word or phrase. So, for instance, the first phrase is A principio (‘from the beginning’), and it lists all the Greek equivalents: ἐξ ἀρχῆς, ἐξ ὑπαρχῆς, τὸ καταρχὰς, τὸ ἐξαρχῆς, ἐκ ῥίζης, τῶν ἀρχῶν, τῶν πρῶτων. You’re right, the font with all the Byzantine ligatures takes some getting used to…