Kendall's tau vs Kendall test

Kendall's tau and Kendall test both are nouns.

Word	Noun	Adjective	Verb	Adverb
Kendall's tau	Yes	No	No	No
Kendall test	Yes	No	No	No

As nouns, Kendall test is a hypernym of Kendall's tau; that is, Kendall test is a word with a broader meaning than Kendall's tau:

Kendall's tau: a nonparametric measure of the agreement between two rankings
Kendall test: any of several nonparametric measures of correlation (used when the assumptions of standard correlational analysis are not met)

Kendall's tau (noun)	Kendall test (noun)
a nonparametric measure of the agreement between two rankings	any of several nonparametric measures of correlation (used when the assumptions of standard correlational analysis are not met)