The journal Econometrica is spelt as I just wrote. The journal Biometrika, however, has a "'k" in place of the letter "c." Biometrika has it right, and Pearson its founder credits Edgeworth for this, "...like a good German he knew that the Greek 'k' is not a modern 'c', and, if any of you at any time wonder where the 'k' in Biometrika comes from, I will frankly confess that I stole it from Edgeworth. Whenever you see that 'k' call to mind dear old Edgeworth."
Ricky (and Edgeworth and Pearson) are correct. Interestingly, Hu McCulloch has a long-ago note on the same topic, in Hu's case dealing with heteroscedasticity vs. heteroskedasticity. It's cutely titled "Heteros*edasticity," and he makes clear that "*" should be "k," for the same Greek root reasons. McCulloch's note is little-known, or perhaps well-known but widely-ignored by philistine econometricians, as "c" is still often used despite the note's publication in one of the profession's most elite and visible journals. You guessed it -- such superb irony -- Econometrica!
Check it out: McCulloch, J. Huston, "On Heteros*edasticity," Econometrica, 53, 1985, p. 483. It's less than one page, authoritative and also humorous, beginning with "The most pressing issue in econometric orthography today is whether heteros*edasticity should be spelled with a 'c' or with a 'k'."