 498 cents)—but in modern use it means any four-note segment of a scale or tone row, not necessarily related to a particular tuning system.The name comes from "tetra" (from Greek—"four of something") and "chord" (from Greek "chordon"—"string" or "note").In ancient Greek music theory, "tetrachord" signified a segment of the greater and lesser perfect systems bounded by "immovable" notes (); the notes between these were "movable" ().