GRC

LSJ

τό, name of the letter χ, IG2². 1491.33, Pl. Ti. 36b, Hellad. ap. Phot. Bibl. p. 530B. ; later written χῖ, v.l. in Hp. VC 1.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
memory