Etymologicum Magnum, the Great Byzantine Etymological Lexicon

The Etymologicum Magnum (Ἐτυμολογικὸν τὸ Μέγα) is the largest Byzantine etymological lexicon, compiled in the mid-twelfth century from the Genuinum, the Gudianum, and related sources. Thomas Gaisford's Oxford edition of 1848 remains the standard complete Greek text, cited by page.

Entries give derivations, dialect forms, and grammatical notes across the whole alphabet. The alternative title Etymologicum magnum auctum is used in the Lasserre–Livadaras synoptic edition. It was the etymologicum most often printed in the West, from Kallierges's editio princeps (Venice, 1499) onward.

The work is a dictionary of Byzantine etymology in Gaisford's text, anonymous like the other great etymologica.