φεῖ
From LSJ
Ἔοικα γοῦν τούτου γε σμικρῷ τινι αὐτῷ τούτῳ σοφώτερος εἶναι, ὅτι ἃ μὴ οἶδα οὐδὲ οἴομαι εἰδέναι → I seem, then, in just this little thing to be wiser than this man at any rate, that what I do not know I do not think I know either
English (LSJ)
τό, name of the letter φ, Callias ap.Ath.10.453d, Hellad. ap. Phot.Bibl.530B.; φεῖ should be restored for φῖ in Pl.Cra.427a, etc.; a pun on φφ = Φιδίς (leg. Φειδίς) in AP7.429 (Alc.).
Frisk Etymology German
φεῖ: {pheĩ}
Grammar: n.
Meaning: indekl. Buchstabenname;
Etymology: nach πεῖ, s.d.
Page 2,999