χεῖ

χ, τό
χεῖ, τό, name of the letter χ, IG 22.1491.33, Pl. Ti. 36b, Hellad. ap. Phot. Bibl. p.530B.; later written χῖ, v.l. in Hp. VC 1.
Liddell, Scott & Jones
A Greek-English Lexicon, 1940
An open-access project