资料来源 : pyDict

次属音占第二位优势的

资料来源 : Webster's Revised Unabridged Dictionary (1913)

Subdominant \Sub*dom"i*nant\, n. (Mus.)
   The fourth tone above, or fifth below, the tonic; -- so
   called as being under the dominant.

资料来源 : WordNet®

subdominant
     n : (music) the fourth note of the diatonic scale