The irregular superlative of the adjective λάλος , “talkative” (see the comparative at lambda 79), here in either masculine accusative singular or neuter nominative/accusative singular. But which?. Apparently neuter, because the neuter article τό before the adjective “clever” has the effect of making the noun abstract (but note that in one lexicon -- Anecdota Graeca I (Bachmann) 287.33 -- it is the masculine τόν ).
This seems to be a bit of scholarly flotsam showing up in various lexica, e.g. Hesychius Lambda239.1 and Photius Lambda205,5, but with the sense of “eloquent” in the Suda, not in the classical meaning, which is illustrated in precisely this form by Euripides, Cyclops 315, where the Silenus [Author, Myth] warns the Cyclops not to bite Odysseus’ tongue when he devours him or he will become “glib and very talkative.” See also Menander fr.164 Kock.