The term 'sword with a three-sided blade' can be summarized as an epee. An epee is a type of fencing sword that has a triangular cross-section and a large bell guard. It is the heaviest of the three weapons used in modern fencing, and is primarily used for thrusting attacks. The epee is the descendant of the dueling sword, and is the only weapon in fencing that allows for simultaneous attack and defense.