The "Tristan chord"; a unique and powerful use of the famous chord, in the most unexpected context. In fact, I discovered it by accident while researching material for my school jazz band. It is clear, unmistakable, and, I suggest, deliberate. Who would ever have thought to look for it in the middle of a jazz arrangement done for the Glenn Miller big band in the 1940's? No one! Which is why it has remained hidden in plain sight for 80 years. (Graphics to follow)