A belief that a religion, a political group, or a school of thought holds on to as one of its basic points. The important part is that a tenet is not a stray opinion — it is a load-bearing belief, one of the few ideas the whole system stands on. If you took it away, the rest would fall over. So we talk about the central tenets of Buddhism, the basic tenets of democracy, a core tenet of the company's approach. It nearly always appears in the plural, and nearly always with a word like basic, central, core, fundamental, or main in front of it. The word is formal and written — you meet it in textbooks, news articles and essays, not in conversation. Notice that saying something is a tenet does not mean you agree with it; a writer can describe the tenets of a group they think is completely wrong. It just says: this is what they hold. There is also a film called Tenet, named for the word's neat spelling, which reads the same forwards and backwards — that is a game with the letters, not with the meaning.