[1] So too, according to Adler, in the Ambrosian Lexicon. In fact two cities of this name are known: one on the Asiatic shore of the Hellespont (Barrington Atlas map 51 grid G4; present-day Maltepe) and Abydos/Ebot in Upper Egypt (Barrington Atlas map 77 grid F4); without much doubt, the former is meant here. (In Hesychius s.v. the gloss is fuller -- 'a Trojan city of the Hellespont'. Latte regards the entry as prompted by Homer, Iliad 2.836, accusative case.) See also alpha 100, sigma 465, and generally OCD(3) s.v.
[2] So too Photius, and cf. Zenobius 1.1, s.v. Ἀβυδηνὸν ἐπιφόρημα (alpha 100). See generally sigma 1330, sigma 1331, sigma 1332.
[3] Homer Iliad 17.584.
[4] So too in the Lexica Segueriana, but in Photius the adjective (in a nominative-case entry) is ἄβυθος , surely correctly; cf. alpha 104. The ultimate source may be Plato, Parmenides 130D, though there too the text is uncertain: perhaps εἴς τιν' ἄβυθον φλυαρίαν (web address 1), though the alternatives include εἴς τινα βῦθον φλυαρίας . At any rate the adjective ἄβυθος is a synonym for ἄβυσσος , "bottomless" (LSJ entry at web address 2).
[5] For an instance in the Suda see pi 71.