In ancient Rome, a tribune was an official chosen by the ordinary people — the plebeians — to protect them from the powerful. His great weapon was the veto: he could stand up and stop a law or an order from harming a citizen, and his person was sacred, so harming him was a crime against the gods. That is the meaning you meet in history class and in books about Rome. Watch out, though, because Rome had another kind of tribune entirely — a military tribune, a senior army officer — and the same English word covers both, so the sentence has to tell you which. Two things grew out of this word. First, in modern political writing, 'a tribune of the people' means anyone who speaks up loudly for ordinary people against those in power; it is a compliment, sometimes a slightly ironic one. Second, it is a favourite name for newspapers — the Chicago Tribune, the International Herald Tribune — for exactly that reason: the paper claims to speak for you. There is also a rarer meaning: a raised platform for a speaker, from the same idea as 'tribunal'.