The term RELATIVE OF A TRUMPET can be answered by two crossword solutions: CORNET (6 letters) and BUGLE (5 letters). A CORNET is a brass instrument similar to a trumpet, but with a conical bore and a more compact shape. It is used in jazz, military, and brass bands. A BUGLE is a brass instrument that is also related to the trumpet, but it has no valves or keys and is used mainly for signaling in military and hunting contexts.