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?