Adler reports the same entry in the unpublished Lexicon codicis Barocciani 50.
Though the Suda manuscripts have r(oubai/oubos (printed by Adler) and r(oubai/oulos, this initial r- is wrong, as Küster realised. See Synesius, Letter 145, lines 11-14, on "a certain Harpokration, holding the rank of assistant's assistant -- for that is how best to interpret the [Latin] term subadiuva [soubadiouba]." See the translation of A. Fitzgerald at web address 1.
Lewis & Short s.v. cites instances in the Theodosian and Justinian Codes.