
1) Leading tone 2) Musical note 3) Note 4) Tone 
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https://www.crosswordclues.com/clue/subtonic

 For example, in the A minor scale (white keys on a piano, starting on A), the subtonic is the note G (in C major this would be B{music|flat}); and the subtonic triad consists of the notes G, B, and D (in C: B{music|flat}-D-F). In music theory, the subtonic chord is symbolized with the Roman numeral {music|flat}VII for a major triad built on the no...
Found on 
http://en.wikipedia.org/wiki/Subtonic

• (n.) The seventh tone of the scale, or that immediately below the tonic; -- called also subsemitone. • (n.) A subtonic sound or element; a vocal consonant, as b, d, g, n, etc.; a subvocal. • (a.) Applied to, or distinguishing, a speech element consisting of tone, or proper vocal sound, not pure as in the vowels, but dimmed and othe...
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http://thinkexist.com/dictionary/meaning/subtonic/
 Sub·ton'ic  adjective  (Phonetics)
Sub·ton'ic  adjective  (Phonetics) 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; --...
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http://www.encyclo.co.uk/webster/S/229
 Sub·ton'ic  noun   1.  (Phonetics)
Sub·ton'ic  noun   1.  (Phonetics) A subtonic sound or element; a vocal consonant, as 
 b , 
 d , 
 g , 
 n , etc.; a subvocal.  
 2.  (Mus.) The seventh tone of the scale, or that immediately below the tonic; -- called also 
 subsemitone . 
Found on 
http://www.encyclo.co.uk/webster/S/229

In music a subtonic is the seventh tone of the scale, or that immediately below the tonic.
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http://www.probertencyclopaedia.com/browse/VS.HTM

[
n] - (music) the seventh note of the diatonic scale
Found on 
http://www.webdictionary.co.uk/definition.php?query=subtonic

subtonic, subtone 1. In music, the subtonic is the lowered seventh degree of the scale, as opposed to the leading tone.  2. The seventh note of the diatonic scale.  3. The seventh tone of a diatonic scale, immediately below the tonic.
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http://www.wordinfo.info/words/index/info/view_unit/2160/2
 leading tone noun
leading tone noun (music) the seventh note of the diatonic scale
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https://www.encyclo.co.uk/local/20974

the seventh tone of a scale, being the next below the upper tonic.
Found on 
https://www.infoplease.com/dictionary/subtonic
  No exact match found.