The rare headword noun (also in other lexica, with the same gloss) is a poetic variant of a(bro/ths; see LSJ s.v. Though it is attested in Sappho and elsewhere, its inclusion here seems to have been prompted by its occurrence in Euripides, Orestes 349 (so Latte on Hesychius s.v.); cf. the scholia there.
cf. generally alpha 70, alpha 73, alpha 86, alpha 87, alpha 88. For the glossing noun see also the gloss at pi 138.