LSJ
Adv., a doubtful word (vv. ll. φύρδην, φρούδην), τὸ φ. καὶ ῥύδην οὐκ οἶδα εἰ ἀνεκτά Poll. 6.175 (fort. φοράδην).
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
[ῡ], adv., = φύρδην, Poll.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)