1) Musical note 2) Note 3) Tone 
In music, the subdominant is the technical name for the fourth tonal degree of the diatonic scale. It is so called because it is the same distance `below` the tonic as the dominant is above the tonic - in other words, the tonic is the dominant of the subdominant. It also happens to be the note immediately `below` the dominant. In the C major s...
• (n.) The fourth tone above, or fifth below, the tonic; -- so called as being under the dominant.
The note or chord on The fourth degree of The major scale. this is Often marked with The Roman numeral IV
Sub·dom'i·nant noun (Mus.) The fourth tone above, or fifth below, the tonic; -- so called as being under the dominant. 
In music the subdominant is the fourth tone above, or fifth below, the tonic. It is so called from being under the dominant.
[n] - (music) the fourth note of the diatonic scale
noun (music) the fourth note of the diatonic scale
the fourth note of a diatonic scale and the chord bulk on that note.
the fourth tone of a diatonic scale, next below the dominant.