The headword is, in the Greek, a one-word adverb with the familiar -then suffix; cf. alpha 311, alpha 379, alpha 1386, etc.etc. It occurs in, and is surely extracted here from, Lucian, Jupiter Tragoedus 10.
A scholion to that passage glosses the word with the comment 'Pentele is a stone made into sculptures amongst Athenians'; i.e. Pentelic marble, from Mt Pentelikon. The lexica (besides the Suda, Adler notes a parallel entry in the Ambrosian Lexicon), as we see, claim a 'city' (polis) called Pentele, but wrongly. Even the deme Pentele claimed by Stephanus of Byzantium s.v. existed, at best, only in a non-constitutional sense.