1. An acoustic instrument consisting of a sounding box with one string and a movable bridge, used to study musical tones.
2. An ancient acoustic device consisting of a single string stretched over an oblong sounding box, used to determine mathematical intervals between musical tones.
3. An instrument for experimenting with 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 on a graduated rule for the purpose of readily changing and measuring the length of the part of the string between them.

4. Etymology: Old French, from Late Latin, from Greek monokhordon, from mono-, "one" + khord, "string".