(1):

(n.) The seventh tone of the scale, or that immediately below the tonic; - called also subsemitone.

(2):

(n.) A subtonic sound or element; a vocal consonant, as b, d, g, n, etc.; a subvocal.

(3):

(a.) Applied to, or distinguishing, a speech element consisting of tone, or proper vocal sound, not pure as in the vowels, but dimmed and otherwise modified by some kind of obstruction in the oral or the nasal passage, and in some cases with a mixture of breath sound; - a term introduced by Dr. James Rush in 1833. See Guide to Pronunciation, //155, 199-202.