ξεῖ

English (LSJ)

τό, indecl., name of the letter ξ, Calliasap.Ath.10.453d, BCH 29.483 (Delos), Phld.P0.2.3 : later

   A ξῖ Luc.Jud.Voc.9, Sch.D.T.p.489 H., etc. ; ξῦ (by assimilation to νῦ), f.l. in Luc. l. c. and AP9.385.14 (Steph. Gramm.).

Frisk Etymological English

(-εῖ = closed -ē)
Grammatical information: n.
Meaning: indecl. letter; Callias ap. Ath. 10, 453d).
Other forms: later ξῖ (Luc.)
Origin: LW [a loanword which is (probably) not of Pre-Greek origin] Semit.
Etymology: After πεῖ = Semit. pē. Schwyzer 140 w. lit.