ˈte.trəˌkȯrd, -ȯ(ə)d noun
Etymology: Greek tetrachordon unit of four tones, from neuter of tetrachordos four-stringed, from tetra- + -chordos stringed (from chordē string) — more at yarn
1. : a musical instrument with four strings
2. : the basic unit of analysis in ancient Greek music consisting of a diatonic or disjunct series of four notes or tones with an interval of a perfect fourth between the first and last and distinguished by the relative position of the half step or steps or quarter tone or tones in the series
3. : the musical interval of a perfect fourth