Definition of subtonics:
(n) :
(music) The note immediately below the upper note of a musical scale.
(adj) :
(phonetics, dated) Of or pertaining to imperfectly articulated sounds or utterances that are inaudible or barely audible, as characterized by Dr. James Rush (Guide to Pronunciation, 1833).
(n) :
(phonetics, dated) An imperfectly articulated sound or utterance, as characterized by Dr. James Rush (Guide to Pronunciation, 1833).