Open to view, or belonging to a people
In current English the adjective public covers several related ideas: something anyone may see, something shared by a community, and something that belongs to government rather than to a private owner. The noun names the people as a whole, or a particular audience, as in the reading public. A park, a listed company, and a scandal that can no longer be contained all sit under the same word because none of them is private.
That split is old. English inherited a Roman contrast between what belonged to the people as a body and what belonged to one person.
The origin of the word public is, in outline, a Latin people-adjective that reached English through both French and the language of schooling, then kept adding civic and commercial senses without dropping the older idea of being out in the open.
Arrival in Middle English
The word is first recorded in English in the late fourteenth century. Early spellings such as publike and publique still show the French look that later English spelling trimmed. Standard dictionaries treat the loan as coming from two routes at once: Anglo-Norman and Old French public or publique, and Latin publicus, which clerks and scholars could take straight from Latin.
The earliest English uses lean toward visibility: an act or fact that is not hidden. In the fifteenth century the word is also found for matters that concern the people at large and for the business of the state. Old English had native ways to talk about communal life, including the adjective folclic. Those forms did not remain the ordinary opposite of private. The Romance loan did.
The noun is younger. The sense of a body of people forming a community or nation is recorded from the early seventeenth century; people in general follows later in that century. The phrase in public, meaning in open view, appears around 1500 and still keeps the spatial sense of a place anyone may see.
From poplicus to publicus
Latin publicus meant of the people, of the state, done for the state, common, even ordinary. Used as a noun it could name a commonwealth or property held in common. The morphology is straightforward once the older form is restored: an adjective in -icus built on the word for the people. That noun is Latin populus, earlier poplus, the same stem English later borrowed again as people and that still sits inside popular and republic, from res publica, the public thing.
The classical shape of the adjective is not the most regular one. Older Latin had poplicus, pertaining to the people. Inscriptions still write POPLICVS and POBLICVS. By the start of the second century BCE the first vowel had become a long u and the inner p had become b, giving publicus. The usual explanation is blending with pubes, the adult male population or manpower of the community. That account is widely accepted, but it is not beyond dispute. Some historical linguists note that a sound change could have produced the same consonants without help from pubes, so the influence of that noun is probable rather than proven.
The suffix is the ordinary Latin marker of belonging. The deeper history of populus is less settled. Proto-Italic poplos is often glossed as army, which would fit an early civic vocabulary in which the people are those who can be mustered. Beyond Italic, sources part company. Some dictionaries take the noun as Etruscan; others suggest a link to an Indo-European root meaning to fill. Neither path is secure, and it is better to stop at the Italic people-word than to force a single prehistoric story.
Romance languages keep the Latin adjective with the usual later sound changes: French public, Spanish publico, Italian pubblico, Portuguese publico. English public belongs to that set, arriving through medieval French and through Latin at the same time.
How the English range widened
Once the loan was in English, its range moved along the same line the Romans had already drawn: from open to observation, toward shared by the community, and then toward done by or for the state. By the 1540s English uses it for things open to all members of a community. Mid-sixteenth-century uses cover acts done on behalf of the community as a whole. Around 1600 it can mean directed to the common interest, even patriotic.
Later combinations show how productive the civic sense became. Public service is attested in the sixteenth century; public interest as common well-being in the seventeenth; public enemy in the eighteenth. Public office, public sector, and public relations are later still. The last of these is a twentieth-century term for managing how an organisation is seen, with an isolated earlier use by Thomas Jefferson that did not yet name a profession. British pub is a clipped public house, first any building open to all, then a licensed inn.
A narrower, now mainly historical sense treated a public woman as a prostitute, on the grim logic of being available to anyone. That usage is a reminder that open to all was never only a civic compliment.
The stock-market sense, a public company or to go public, extends accessibility to buyers of shares. Programming later reused the same contrast: a public method is one the rest of the program may see.
The mismatch with people
If public looks slightly off from people, the mismatch is already Latin. Poplicus was reshaped, very likely under the pull of pubes, long before English met the word. Republic still shows the civic pairing more plainly, the public thing, while public itself carries both political belonging and the everyday fact of being out in the open. Those two meanings have never quite come apart, which is why a public park and a public figure still share a name.