RESONANCE (5 letters) The term REPEATED SOUND can be described by two crossword solutions: ECHO (4 letters) and RESONANCE (5 letters). An ECHO is a sound that is heard again after it is produced, usually due to reflection of sound waves off a surface. RESONANCE is the reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighboring object. Both terms refer to the repetition of sound, either through reflection or vibration.