= Cyril, Photius beta14, Hesychius beta25, [Zonaras] 375.9. The headword is unattested elsewhere. It is glossed as neuter nominative/accusative singular (rather than masculine accusative).
The word may derive from a root that shows up in terms for 'god' in Old Persian (baga-; cf. Russian bog), seen perhaps in the Persian proper name Bagaios (beta 12, pi 116, and cf. a man of the same name in the family of Pharnaces, Persian satrap of the Hellespont -- Plutarch, Alcibiades 39 -- though some mss read Magaios rather than Bagaios). According to Hesychius beta22, *bagai=os was also the Phrygian name for Zeus, and the text of that entry also includes the glosses 'great, mighty, swift'; however, Latte brackets these glosses as belonging properly to an entry on balaio/n (beta132). Another possibility for our headword is that it is an adjectival derivative from ba/gos which Hesychius epsilon26 defines as a Lakonian term for king and general, but both Latte and Chantraine believe this is a mistake on the lexicographer's part (see also Chantraine's skeptical comments on the possible relation between this term and the Iranian baga-). Finally, perhaps the likeliest possibility is that the entry is corrupt. Latte suggests that the headword is a misspelling (influenced by Late Greek pronunciation?) of bai+o/n ('measuring stick') and that the gloss originally was me/ga ba/ktron ('big staff').