Alternative spelling of chi (uppercase Χ, lowercase χ), the 22nd letter of the Greek alphabet.
1898, Claude Reignier Conder, The Hittites and Their Language, W. Blackwood and Sons, page 249:It is known, from the existence in his time1 of the Delphic tripod, that all these letters existed in 480 B.C. ; but on that monument the Khi and Psi differ from the forms used later.
1963, Thomas Albert Sebeok, Current Trends in Linguistics, Mouton, page 404:The letters upsilon, phi, khi, psi, δ were Greek additions
2006, Jonathan M. Hall, A History of the Archaic Greek World, Blackwell Publishing, page 57:Greek scripts display notable local characteristics — principally with regard to the shape of letters but also in the matter of the phonetic values attributed to signs such as san, sigma, khi, and psi.----
