= Harpocration s.v. (A2 Keaney).
The point is that the alpha prefix intensifies, rather than negates as it usually does: LSJ entries for ἄβιος (A) and (B) at web address 1. On the different alpha prefixes, see LSJ.
[1] Antiphon (the sophist) B87 F43 Diels-Kranz.
[2] Homer, Iliad 11.155 (web address 2): ἐν ἀξύλῳ... ὕλῃ , of a forest fire falling in "a wood with much dead timber," and thus spreading rapidly. On the meaning of this adjective see Lexikon des frühgriechischen Epos I (fasc. 6, 1969) 974-75. (Although LSJ correctly defines ξύλον as 'timber', the entry there for ἄξυλος erroneously assumes alpha privative and is misleading.)