A tenet is a principle or belief honored by a person or, more often, a group of people. "Seek pleasure and avoid pain" is a basic tenet of Hedonism. "God exists" is a tenet of most major religions.
Tenet is pronounced "ten’it." The word evolved from the Latin tenere "to hold." The noun tenet is an opinion or doctrine one holds. It usually refers to a philosophy or a religion, but it doesn't have to — for instance, Eastern medicine has different tenets from Western medicine. One of the central tenets of succeeding in the workplace is that a good offense is the best defense.