单词：tetrachord
音标：['tetrәkɒ:d] ；
n. 四音音列, 四弦琴
n. A scale series of four sounds, of which the extremes,
or first and last, constituted a fourth. These extremes were immutable;
the two middle sounds were changeable.
or first and last, constituted a fourth. These extremes were immutable;
the two middle sounds were changeable.