1. A musical instrument with eight strings.
Usage: rare; historical
2. In music theory, a series or scale of eight notes or tones.
Usage: technical; music

Examples

• The ancient octachord was an early stringed instrument used in Greek music.
• Medieval theorists studied the octachord as a fundamental musical interval.
• An octachord consists of eight consecutive pitches in the diatonic scale.
• The octachord formed the basis of many early musical systems.