Public means open to everybody, or belonging to everybody, rather than to some. A public park, public transport, a public meeting.
It is also the noun for people in general, always with the: the public, a member of the public. Two British traps are worth naming. A public school in England is a famous fee-paying private school — the opposite of what the words suggest, and of what public school means in America. And a public house is a pub, which is why the sign says one thing and everybody says the other. Note in public, meaning where people can see, and go public, meaning either to reveal something or to float a company.
1adjectivepublicOpen to or shared by everybody.
“It is a public footpath and anyone may use it.”
2noungeneralPeople in general.
“The gardens are open to the public at weekends.”
3adjectiveprovidedProvided or run by the government.
“Public transport is cheaper than driving in.”
4adjectiveknownKnown to everybody rather than private.
“The argument became public within a day.”
Too few real examples of this word to estimate which sense is commonest.
public is a quality of being open to all.
Latin publicus meant of the people, from populus, the people — the same root as popular, population and pub. The English word has always meant the shared thing, which is why it grates so much that a public school is not one.
Proto-Indo-European
*pleh₁- — to fill
Proto-Italic
*poplos — army
Latin
pūblicus — of or belonging to the community, people, or state; general, public
Old French
public — (adjective) generally observable, public; relating to the general public; official; (noun) community or its members collectively; nation, state; audience, spectators collectively
Middle French
public
Anglo-Norman
public
Middle English
publik
English, today
public
Built from
The adjective and noun are derived from Late Middle English publik, publike (“(adjective) generally observable, public; relating to the general public or public affairs; (noun) a generally observable place or situation”), from Anglo-Norman public, publik, publique, Middle French public, publique, and Old French public (“(adjective) generally observable, public; relating to the general public; official; (noun) community or its members collectively; nation, state; audience, spectators collectively”) (modern French public, publique obsolete); and from their etymon Latin pūblicus (“of or belonging to the community, people, or state; general, public”), an alteration of poplicus (influenced by pūbēs (“adult men; male population”)), from poplus (“community; the people, public; nation, state”) (later populus; from Proto-Italic poplos (“army”); further origin uncertain, possibly from ett - or from Proto-Indo-European pleh₁- (“to fill”)) + -icus. Related to people, populus etc. The Middle English word displaced native Old English ceorlfolc and folclic. The verb is derived from the adjective.
Etymology from Wiktionary, CC BY-SA