Definition of "monochord"

monochord

noun
plural monochords
1. 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.
  Quotations
  If a musician were going to give a lecture upon the mathematical part of his art, he would find a very elegant substitute for the monochord in the Chinese kin.
  1840, Elijah Coleman Bridgman, Samuel Wells Williams, The Chinese Repository, page 40
2. A stringed instrument with only one string.