A word that covers everything, and then a rank
In modern English, general is the everyday opposite of specific. A general rule is meant to hold for a class of cases. A general store stocks many kinds of goods. A general hospital treats more than one disease or group of patients. The same word also names a senior military officer. Those uses look far apart, yet they share a single idea: authority or application that is not limited to one corner of a field.
The origin of the word general is a borrowing, not a native Old English inheritance. Writers in the early thirteenth century already used it as an adjective for what belongs to a whole kind rather than to a special case. The Oxford English Dictionary points to evidence around 1230 in the Ancrene Riwle. Other historical dictionaries place the first English uses a little earlier, about 1200. The dates are close; the period is early Middle English either way.
From French and Latin into Middle English
The immediate English form is Middle English general (sometimes spelled generall). Behind it stand Anglo-Norman and Middle French general, and, behind those, Latin generālis. Sources do not tell exactly the same story about the last hop. Some treat the English word as coming through French and also, in learned use, straight from Latin. Others skip French and write only Latin to Middle English. The safest account is that English took a Romance adjective that was already Latin in origin, and that clerks who knew Latin could reinforce the form without needing a French speaker in the room.
Latin generālis was built in a transparent way. The noun genus, genitive generis, meant a stock, race, family, or kind. The suffix -ālis made an adjective: of a kind, belonging to a class as a whole. Roman writers contrasted that sense with specialis, the word for what is particular. Lewis and Short records generālis both as of a species and, more often from the Augustan period onward, as relating to all, set against the single instance. That pair—general versus special—is still the spine of the English adjective.
Kind, birth, and a deep Indo-European root
Genus itself is older than Latin literature. It continues a Proto-Italic genos and, further back, a Proto-Indo-European noun reconstructed as ǵénh₁os, from the verbal root ǵenh₁- (also cited as gene- or genə-), whose core sense is to beget or give birth. Words from that root tend to talk about offspring, lineage, and then, by a short step, about classes of things that belong together.
English is full of later Latin and French cousins from the same family: generic, generate, generation, gender, genre, generous, genesis. Native Germanic relatives from the same root include kin and kind. Greek genos is a parallel, not an ancestor of the English word. The military noun general in languages such as French général, Spanish general, Italian generale, and German General is the same Latin adjective, later used as a title. German also has the learned adjective generell, a separate later borrowing with the logical rather than the rank sense.
None of this is folk etymology. The -al ending is the Latin suffix, not an English invention glued onto a mystery stem.
How the meaning widened
The first English uses stay close to the Latin contrast: wide application, generic, affecting all, as opposed to something special. By the late fourteenth century the adjective was being attached to office names to mark jurisdiction that ran across a whole domain rather than a local one. That is why English still has titles in which general follows the noun: attorney general, solicitor general, surgeon general, secretary general. The word order is a Romance pattern kept in legal and institutional English, the same habit that gives court martial and notary public. In general, meaning as a rule or taken as a body, is recorded from the same late-fourteenth-century stretch. General rule, a principle for an art or science as a whole, appears around 1400.
From the sixteenth century the adjective also covers a looser sketch: only the main points, not the particulars. That is the general of a general outline or a conversation that has become general after a sharp remark. Another sixteenth-century development is the miscellaneous sense, as in general goods: not of one trade or class.
The noun started as a name for a whole class of things or persons, or for a broad truth—the general as opposed to the particular. That use is now rare except in set contrasts. What replaced it in everyday speech is the clipped military title.
When a captain became a general
From the late fourteenth century, general in titles already meant chief, with authority over a wide command. In French the full style was capitaine général: a captain whose charge was not a company but an army or a theatre. English borrowed the compound; the OED has captain-general from the early sixteenth century. By the 1570s speakers were shortening the phrase to general for the commander of an army. Wikipedia and historical rank lists treat captain general as one of the first military settings in which general marked overall command. Later ranks—lieutenant general, major general, brigadier general—keep the same marker so that they are not confused with a lieutenant or a major of ordinary grade.
Other specializations are later and narrower. A general hospital, recorded in the eighteenth century, is not limited to one class of patient or illness. An American general store, from the early nineteenth century, sells a range of goods. In the United States a film rating G has stood, since 1966, for audiences in general. Older English also used general for the head of some religious orders, for a maid-of-all-work (a general servant), and, in naval history, sometimes for a senior sea officer. Those last senses have mostly faded.
A cousin hiding in plain sight
The military rank feels like a different word until the title is unpacked: the officer whose brief is the whole force, not a single post. That is still the Latin adjective talking. A quieter reminder sits in native English. Kind as a class or sort, and kin as family, grew from the same Indo-European root as Latin genus. When we say a general kind of thing, two branches of one family meet in a single phrase.