[1] Same glossing in Eudemus and ps.-Zonaras. The headword is dative plural of this adjective, quoted from somewhere -- very probably from its only occurrence outside lexicography: Apollonius Rhodius, Argonautica 3.1386 (ἀγχούροισιν ), the scholia to which have the gloss "neighbours".
[2] This etymology is accepted in LSJ s.v.