Short answers, pulled from the story.
Hesychius of Alexandria was a Greek grammarian who probably lived in the 5th or 6th century AD. He compiled a lexicon of more than 50,000 unusual and obscure Greek words, drawing on the work of earlier lexicographers including Diogenianus, Aristarchus of Samothrace, Apion, Heliodorus, and Amerias.
The lexicon is titled "Alphabetical Collection of All Words" (Synagoge Pason Lexeon kata Stoicheion) and contains more than 50,000 entries. Each entry explains a peculiar or obscure Greek word or phrase, often citing the ancient author who used it or the region of Greece where it was current.
Hesychius preserved many words not found in any other surviving ancient Greek text, making his lexicon vital for studying ancient Greek dialects, obscure Balkan languages such as Albanoid and Thracian, and for reconstructing Proto-Indo-European. His explanations of epithets also reveal facts about the religion and social life of the ancients.
The single surviving manuscript, catalogued as Marc. Gr. 622, is preserved in the Library of Saint Mark in Venice. It dates to the 15th century and is described as deeply corrupt due to transmission errors accumulated over centuries.
The first printed edition appeared in 1514, produced by Marcus Musurus at the press of Aldus Manutius in Venice. Modest revisions followed in reprints of 1520 and 1521.
A modern edition was published under the auspices of the Royal Danish Academy of Fine Arts in Copenhagen. Kurt Latte began it, with volume 1 published in 1953 and volume 2 posthumously in 1966. Peter Allan Hansen and Ian C. Cunningham completed the work with volume 3 in 2005 and volume 4 in 2009.