What is the etymology of halakhah?
The meaning of הלכה is understood to mean משפט and דת, to use the definition supplied by R. Elijah Levita in his תשבי. It was usually understood to be derived from the Hebrew root הלך, to go.
(For an ancient source, see Targum Onkelos, which sometimes translates the term משפט as הלכתא. For example, it translates Gen. 40:13's כַּמִּשְׁפָּט הָרִאשׁוֹן as כהלכתא קדמיתא, Ex. 21:9's כְּמִשְׁפַּט הַבָּנוֹת as כהלכת בנת ישראל , but Ex. 21:1's וְאֵלֶּה הַמִּשְׁפָּטִים is translated as ואלין דיניא.)
The question is, how did a root meaning to go turn into the term for Jewish law? Or did it?
There is an interesting footnote in R. Saul Lieberman's essay on the "publication of the mishnah"1 in Hellenism in Jewish Palestine, pg.83-84. I present it below:
As you can see, he notes that in the Aramaic portion of Ezra there is a term הֲלָךְ which meant toll.2 Gesenius identified Ezra's הֲלָךְ with ilku from the Babylonian for tax. Furthermore, in Aramaic a land tax was called הלכתא.
In short, the word halakhah (in Hebraized form) may have Aramaic roots in the sense of a fixed rule, from a fixed land tax.
Incidentally, what R. Lieberman calls its Latin equivalent, regula, R. Elijah Levita gives לייציון as the לע"ז. I'm assuming he meant German? Although it does look vaguely French. A European Latin legal term? Does anyone know what לייציון refers to?
1 I believe he deliberately used the term "publication" anachronistically, to buttress his view that the mishnah remained oral, rather than written, and could be "published" in that form. See Menachem Mendel's here and here.
2 He called it tax, but I simply went with the 1917 JPS's "toll," as per my practice to use that translation unless I have a specific reason not to.
3 In case you are wondering why I restate his comments which are in the image, it's because I want the discussion to be archived by search engines.