What is the X in X-mas?
fourteenth letter of the Greek alphabet.
xi (zī, sī, ksē)
Symbol ξ The 14th letter of the Greek alphabet.
A VLSI design language.
["The Circuit Design Language Xi", S.I. Feldman, unpublished memo, Bell Labs, 1982].
[Mentioned in Computational Aspects of VLSI, J.D. Ullman, CS Press 1984].