GRC

LSJ

τό, indecl., name of the letter ξ, Callias ap. Ath. 10.453d, BCH 29.483 (Delos), Phld. P 0.2.3 ; later ξῖ Luc. Jud. Voc. 9, Sch. D.T. p. 489 H., etc. ; ξῦ (by assimilation to νῦ), f.l. in Luc. l.c. and AP 9.385.14 (Steph. Gramm.).
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
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