For heaven's sake, eta, how fascinating; I wish it gave a few more details, such as how many times a section had to be walked before it became a purlieu.

By comparison:
mi·lieu ( P ) Pronunciation Key (ml-y, m-ly)
n. pl. mi·lieus or mi·lieux (-ly)
An environment or a setting.

[French, from Old French, center : mi, middle (from Latin medius. See medhyo- in Indo-European Roots) + lieu, place (from Latin locus).] (AHD) Also AHD:

pur·lieu ( P ) Pronunciation Key (pûrly, pûrl)
n.
1. An outlying or neighboring area.
2. purlieus Outskirts; the environs.
3. A place that one frequents.

[Middle English purlewe, piece of land on the edge of a forest, probably alteration (influenced by Old French lieu, place), of porale, purale, royal perambulation from Old French porale, from poraler, to traverse : por-, forth (from Latin pr-. See pro-1) + aler, aller, to go; see alley1.]