'Subdominant' definitions:

Definition of 'subdominant'

From: WordNet
noun
(music) the fourth note of the diatonic scale

Definition of 'Subdominant'

From: GCIDE
  • Subdominant \Sub*dom"i*nant\, n. (Mus.) The fourth tone above, or fifth below, the tonic; -- so called as being under the dominant. [1913 Webster]