TITLE: Chi-square or chi-squared?
QUESTION [11 upvotes]: The $\chi^2$ test/distribution is referred to as either "chi-square" (more frequently) or else "chi-squared" (less frequently).
What is the history behind the name?
Footnote 2 in this paper by Peter Scott makes the following claim (without any corroboration):

The notation of $\chi^2$ is traditional and possibly misleading. It is a single statistical variable, and not the square of some quantity. It is therefore not chi squared, but chi-square. The notation is merely suggestive of its construction as the sum of squares of terms. Perhaps it would have been better, historically, to have called it $\xi$ or $\zeta$.

The Wikipedia article "Pearson's chi-squared test" states that it was first investigated by Karl Pearson in this paper from 1900, in which he apparently just uses the notation $\chi^2$. More historical information can be found in Plackett's 1983 article, "Karl Pearson and the Chi-squared Test".
Some evidence that suggests that it was first called "chi-square", and only later was "chi-squared" used, is the fact in MathSciNet the first paper with "chi-squared" in the title was published in 1958, whereas "chi-square" is used in the title of articles from 1940 onwards.

Who first used the term "chi-square" in print?
And why was "chi-square" not "chi-squared" used?
And when was "chi-squared" first used in print?

REPLY [2 votes]: As a matter of fact Pearson's original paper uses $\chi$ alone (without the exponent) frequently.  Equation $(i)$ in the paper defines $\chi^2$ but the text speaks of using the equation to find $\chi$.  Given this background, it seems absurd to say that $\chi^2$ is not a square.