Henry George Liddell, Robert Scott, A Greek-English Lexicon

A.“ἀπὸ ἄλφα ἕως .ω.” Gloss.iii 283 (ix A. D.); thence used as a symbol of the end, the last, ἐγώ εἰμι τὸ ἄλφα καὶ τὸ ὦ (not τὸ ὦ μέγα) Apoc.1.8, al.:—as a numeral ώ = 800, but ωνυμ = 800,000. The epichoric Att. and other alphabets of the Inscrr. had used o in differently to represent the sounds of the later ο and ω : Ω is a differentiated form of ο, and, though usu. = ω, was used in the Ionic islands of Paros, Thasos, and Siphnos with the value ο, while O or O represented the sound ω. The name of the letter was τὸ ὦ (perispom. acc. to Hellad. ap. Phot.p.530B.), cf. Achae.33.3, Pl.Phdr.244d, Cra. 420b, Tht.203c: after the loss of the distinction betw. long and short vowels, ο and ω had the same pronunciation; they begin to be confused in Papyri of iii B. C. (“οἰκωνόμου” PRev.Laws 50.22 (iii B. C.)), but the name ω μέγα appears first in later Greek, Theognost.Can. 13; “κατὰ σχῆμα διπλοῦ ω_ ἤτοι μεγάλου” Eust.869.26; “οἱ δὲ περὶ Ἀρίσταρχον αὐτὸ τὸ ποτήριον ω_ μέγα εἶναί φασιν, ὁποῖν ἴσως τὸ κατὰ δύο υ_ ἐσχηματισμένον” Id.869.29; ἐν τῷ ω_ μεγάλῳ under omega (in a lexicon), Id.1828.49: “διὰ του^ ω_ μεγάλου” Hdn.Epim.208.