Stretch in space and in time
In ordinary English, long is the everyday measure of extent. A river can be long. So can a meeting, a vowel, or a wait. The same shape of the word works as an adverb: people stay long, have long known a fact, or ask how long something will take. A separate-looking verb, to long, means to yearn. Those uses feel like different words, but most of them grew from one inherited Germanic adjective that already mixed distance with duration.
Native, not borrowed
The origin of the word long is inheritance, not a medieval loan. In Old English, well before 1150, the adjective appears as lang and also as long. It already meant having great linear extent, lasting a long while, and, more freely than today, being tall. The adverb lange or longe is equally old. From there the form runs back through Proto-West Germanic lang to Proto-Germanic langaz, the same stock that yields German and Dutch lang, Old Norse langr, Swedish lång, Danish lang, and Gothic laggs.
That distribution matters. A word shared by Gothic, Norse, and West Germanic was already in the family before English existed as a separate language. Latin longus looks almost the same, and it later supplied English with learned relatives such as longitude, elongate, and prolong. It is a cousin, not the parent. The two adjectives meet further back, in Indo-European, not in a borrowing from French or church Latin.
A deep root with a disputed shape
Most reconstructions take Germanic langaz from a Proto-Indo-European adjective on the order of dlongʰos, meaning long. That form is usually grouped with a wider set of words for length and lastingness, often placed under a root reconstructed as del-. Latin longus belongs in that set. So do Sanskrit dīrgha, Iranian forms of the darga- type, Old Church Slavonic dlŭgŭ and later Slavic adjectives such as Russian dolgij, Lithuanian ilgas, and Greek dolikhos. Hittite taluki- is often listed with them as well.
The relationship is widely accepted; the exact morphology is not. Some of these words look as if they contain a nasal infix. Others do not. Greek and the Indo-Iranian forms sit at a different vowel grade. Handbooks tend to say that the family is real and then refuse a single tidy formula. That caution is the right one. The English adjective sits securely in Germanic. Beyond Germanic, the map of related forms is still a sketch.
Why the vowel became o
The older English spelling lang still shows the Germanic a. In the south, that vowel regularly became o before certain clusters, including ng. The same local change appears in pairs such as band and bond, and in West Midlands dialect lond and hond beside standard land and hand. In some accounts of the word, the vowel was also lengthened before ng and later shortened again in southern Middle English. North of that line the older vowel survived. Scots still has lang. Some northern English speech kept lang well into the twentieth century, though that form is now rare.
Old French long, itself from Latin longus, may have given the southern o-spelling an extra push. If it did, it was reinforcement, not replacement. The native adjective was already in English. The French word and the English word look alike because they are distant relatives, not because one replaced the other.
Senses that held, and one that slipped
From the earliest English records, long measured both space and time. Duration is not a late metaphor painted onto a spatial word. Old English already used the adjective for something drawn out in time, sometimes with a serious or weighty tone. The spatial sense remains the core: a long road, a long table, a long way. The time sense is equally ordinary: a long day, a long book, no longer.
Height is the sense that has faded. Old English could call a person lang where modern English prefers tall. That older use survives in a few regional and dated phrases — the pairing of the long, the short, and the tall is a fossil of it — but it is no longer the default for human stature.
Later English kept adding specialized uses without rewriting the old core. Around the year 1000, a long vowel was one held for more time; the label stuck even after English vowels stopped being distinguished mainly by duration. Finance borrowed the spatial image: to be long a stock is to hold it in hope that the price will stretch upward, the opposite of being short. Sporting English has long ball, first in cricket in the mid-eighteenth century, and long jump from the nineteenth. American slang long on, meaning well supplied with something, is recorded from about 1900.
Yearning and the season of longer days
Beside the adjective sits the verb to long, to yearn. It comes from Old English langian, which could mean to grieve for or desire, and also, more literally, to grow long or lengthen. Many etymologists treat that verb as built on the same Germanic adjective: desire as a stretching toward what is not yet reached. German verlangen, to desire, is a close relative, as are Old Norse langa and related verbs in continental West Germanic. A competing analysis traces the Germanic verb to a different Indo-European root connected with movement and ease. The English surface history is clear either way. Langian is old, native, and already emotional in the earliest texts.
Other native words keep the same stem in view. Length is the noun. Along goes back to Old English andlang, through the whole length of something. Linger is connected with an Old English verb meaning to prolong. Even Lent belongs here in a roundabout way: Old English lencten named spring, and then the fast before Easter, as the season when days grow longer.
Because English long and Latin longus are so close in form and meaning, it is easy to assume a borrowing. The chronology and the Germanic cognates rule that out. English had the word before the Norman Conquest. Gothic had laggs far from any French influence. What Latin did contribute is a parallel learned vocabulary sitting beside the old native adjective.
The northern relic makes the point in one syllable. Where standard English rounded the vowel, Scots kept lang. That older shape is still the Germanic adjective, still measuring distance and duration, and still unborrowed.