Likewise, according to Adler, in two entries of the Ambrosian Lexicon (92 and 55 respectively).
The place in question is better known as Gibeon, present-day el Jib in the West Bank, some 8 km NW of Jerusalem; Barrington Atlas map 70 grid G2). In the Septuagint (e.g. Joshua 9:9) and other Greek sources (e.g Josephus, Jewish Antiquities 7.11 (283)) it is *gabaw/n, Gabaon; the lexicographers' Gabao is either a variant (or corruption) of that, or else its (attested) accusative case.
The ethnic term given here *Gabaoni=tai ('Gabaonites' or 'Gibeonites') is attested in e.g. 2 Kings 21:2 LXX for the inhabitants of Gibeon. This is perhaps the origin (via ps.-Herodian 3.1.93.7) of Stephanus of Byzantium's reference to a city in Galilee called "Gabaoupolis", with an ethnikon "Gabaoupolites"; he cites Josephus, who in fact refers (Jewish Antiquities 6.7 (105)) not to "Gabaoupolis" but "Gabaon polin" ('Gabaon city') which may be a reference to Gaba or Gabaa -- both, like Gibeon, sited within the territory of the tribe of Benjamin (cf. Kallai 1986: 398-404).
Curiously, none of these places is anywhere near the region of Galilee. Perhaps there is confusion in our sources with the Gaba(a) near Galilee mentioned by Josephus, Jewish War 3.3 (36).