noun, noun which may take the genitive case particle 'no'
submediant
In music theory, the sixth scale degree; also used attributively with の to describe chords or keys built on that degree.
ハ長調の下中音はイ音です。
The submediant of C major is A.
この曲は下中音の和音で始まる。
This piece begins with the submediant chord.
属音 is the dominant (fifth scale degree), a fifth above the tonic; 下中音 is a third below the tonic.
Compound of 下 (ka, 'below'), 中 (chū, 'middle'), and 音 (on, 'sound, note'). The term is a calque from Western music theory, where the submediant lies midway between the tonic and the subdominant below.