Noun
The sixth tone of the scale; the under mediant, or third below the keynote; the superdominant.
Source: Webster's dictionaryThe Dorian mode ( About this sound listen ( help · info ) ) corresponds to the natural minor scale with the submediant (sixth scale degree) raised a semitone. Source: Internet
The new flat is placed on the subdominant (fourth degree) for major keys or submediant (sixth degree) for minor keys. Source: Internet