Monochord
Monochord , noun
[Latin monochordon, Greek {not transcribed}, from {not transcribed} with but one string; {not transcribed} only, single + {not transcribed} string: compare French monocorde. See Chord, and compare Mainchord.]
(Music) 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.