Same entry, according to Adler, in the Ambrosian Lexicon (44).
The headword adjective is attested most commonly in the plural; see e.g. Homer, Iliad 13.41.
LSJ s.v. (web address 1 below) notes that the initial alpha of the word is sometimes (as here) copulative but can also (e.g. in Apollonius Rhodius) be privative, i.e. noiseless.