noun. An acoustic instrument consisting of a sounding box with one string and a movable bridge, used to study musical tones.

noun. An acoustical instrument, invented at a very early date in Egypt or Greece, consisting of a long resonance-box over which a single string of gut or wire is stretched, the vibrating length, and thus the pitch, of which is fixed by a movable bridge.

noun. An instrument for experimenting upon the mathematical relations of musical sounds. It consists of a single string stretched between two bridges, one or both of which are movable, and which stand upon a graduated rule for the purpose of readily changing and measuring the length of the part of the string between them.

noun. A musical instrument for experimenting with the mathematical relations of musical sounds, consisting of a single string stretched between two bridges, one or both of which can be moved, and which stand upon a graduated rule for the purpose of changing and measuring the length of the part of the string between them.

"It was afterward known as the "monochord," and by its means all the ancients demonstrated the ratios of the octave, fourth and fifth, as we will later see."