Adler reports the same entry in the Ambrosian Lexicon, and (more helpfully) that ms.V adds the gloss o)/no(ma), i.e. name. If this is correct, it might be the genitive case of Odion; cf. generically (e.g.) delta 1335, eta 548, kappa 20, kappa 403, lambda 316, mu 200, mu 213, nu 580, xi 38.