Origin and history of furlong

Middle English furwe, forowe, forgh, furch, from Old English furh "furrow, trench in the earth made by a plow," from Proto-Germanic *furkh-, which is reconstructed (Watkins) to be from PIE *perk- (2) "to dig, tear out" (source also of Latin porca "ridge between two furrows," Old Irish -rech, Welsh rhych "furrow"). Germanic cognates include Old Frisian furch "furrow;" Middle Dutch vore, Dutch voor; German Furche "furrow;" Old Norse for "furrow, drainage ditch."

The general meaning "narrow trench or channel" is from early 14c. In reference to a deep wrinkle on the face, by 1580s.

Old English lang "having a great linear extent, that extends considerably from end to end; tall; lasting," from Proto-Germanic *langa- (source also of Old Frisian and Old Saxon lang, Old High German and German lang, Old Norse langr, Middle Dutch lanc, Dutch lang, Gothic laggs "long").

The Germanic words perhaps are from PIE *dlonghos- (source also of Latin longus "long, extended; further; of long duration; distant, remote," Old Persian darga-, Persian dirang, Sanskrit dirghah "long"), from root *del- (1) "long" (source also of Greek dolikhos "long," endelekhes "perpetual"). Latin longus (source of prolong, elongate, longitude, etc.) thus is probably cognate with, but not the source of, the Germanic words. The word illustrates the Old English tendency for short "a" to become short "o" before -n- (also retained in bond/band and West Midlands dialectal lond from land and hond from hand).

Also in Old English in reference to time, "drawn out in duration," with overtones of "serious." The old sense of "tall" now appears to be dialectal only, or obsolete. For long "during a long time" is from c. 1300. To be long on something, "have a lot" of it, is from 1900, American English slang. A long vowel (c. 1000) originally was pronounced for an extended time. Mathematical long division is from 1808. Sporting long ball is from 1744, originally in cricket. Long jump as a sporting event is attested from 1864. A long face, one drawn downward in expression of sadness or solemnity, is from 1786. Long in the tooth (1841 of persons) is from horses showing age by recession of gums (but not in this sense until 1870). Long knives, name Native Americans gave to white settlers (originally in Virginia/Kentucky) is from 1774, perhaps a reference to their swords. Long time no see, supposedly imitative of American Indian speech, is first recorded 1919 as Chinese English.

mid-14c., stadie, "a foot race, a racecourse;" early 15c., "ancient measure of distance," from Latin stadium (plural stadia) "a measure of length" (variously reckoned, commonly one-eighth of a Roman mile or a little over 600 standard English feet; translated in early English Bibles by furlong); also "a stage, a station; a course for foot-racers;" from Greek stadion "a measure of length; a race-course, a running track," especially the track at Olympia, which was one stadion in length.

"Originally the distance between successive stations of the shouters and runners employed to estimate distances," extended to the course itself [Century Dictionary].

According to Barnhart, the notion in the Greek word might be "fixed standard of length, that which stands fast" (from stadios "firm, fixed," from PIE root *sta- "to stand"). Beekes does not seem to connect them, however, and allows rather that stadion is "Perhaps an original folk-etymological transformation" of Greek spadion "race-track," which is a derivative of span "to draw up, pull" (compare spasm), perhaps on the notion of "the lengthy one." If so, the form might be influenced by stadios.

The form in English has been re-Latinized from early modern stade. The meaning "running track" in English is recorded from c. 1600 and was extended to mean "large, open oval structure with tiers of seats for viewing sporting events" (1834). The classical sports stadiums had sloping banks of seats for spectators along two sides and one end.