public

The root public goes back to Latin pūblicus, an adjective meaning 'belonging to the people' — that is, to the whole community rather than to any single private person. From the very beginning, the key contrast was pūblicus vs prīvātus: things that belong to everyone (roads, baths, treasury, the law courts) versus things that belong to one household. That ancient split between public and private is still the heart of every word in this family.

The form pūblicus is itself a small mystery. It clearly grew out of populus, 'the people' (the same root that gives us population, popular, public's cousin people). An older form was poplicus, 'of the populus.' But along the way the word was reshaped under the influence of pūbēs, meaning 'the adult population, grown men' — the people old enough to vote and bear arms. So pūblicus ended up meaning, roughly, 'belonging to the adult body of citizens.' You don't need to remember pūbēs; just hold onto the core: public = of the people as a whole.

English took pūblicus and built a tight family around the citizen idea. Public itself does double duty: as an adjective it means 'open to all, shared by the community' (public park, public school, public opinion); as a noun, the public is the people themselves. From there the family spreads by adding suffixes. Publicly is simply 'in a public way' — openly, where everyone can see. Publicity is the state of being public: public attention, and then the deliberate effort to attract it (a publicity stunt). Publicize is the verb: to make something public, to spread it widely.

Two members are about putting words into the open. Publication comes from pūblicāre, 'to make public' — and when you make a book or article public, you publish it. (The verb publish itself reached English through Old French publier, which is why it lost the hard -c-; same root, French detour.) A publication is therefore both the act of making something public in print and the printed thing itself — a magazine, a journal, a paper.

The most surprising member is republic. It comes from the Latin phrase rēs pūblica — literally 'the public thing' or 'the public affair' (rēs = thing, matter; pūblica = public). To the Romans, the rēs pūblica was the state itself understood as the common property of all citizens, as opposed to something owned by a king. So a republic is, at root, a country that belongs to its people rather than to a monarch. The English word commonwealth ('common-weal,' the common good) is a native attempt to translate exactly this idea.

A few cousins lurk nearby. A pub is just public house clipped down to one syllable — a house open to the public for drinking. A publican in modern British English is the keeper of a pub; in the Bible it meant a Roman tax-collector (one who handled public revenue). And right next door sits the family of populus — people, popular, population — the very root that pūblicus grew out of. Across the language barrier, Greek offers the same idea twice over: dēmos 'the people' (democracy) and koinos 'common, shared' (the cousin of Latin commūnis, community).