Diatonic: Refers to individual notes and harmonies staying within a given key (e.g.: C Major, or C minor).
Dominant: The fifth (5th) note in a Major or minor scale; or The diatonic triad rooted on the fifth (5th) note in a Major or minor scale.
Dominant Seventh: The diatonic seventh chord rooted on the fifth (5th) note in a Major scale; or The diatonic seventh chord rooted on the seventh (7th) note in a natural minor scale. Also known as a Major minor Seventh Chord
Dreadnought: Large bodied steel-string acoustics which feature broad waists and a resonant bass tone when played. Dreadnoughts are played by folk, bluegrass and country musicians. Guitar manufacturer Martin produceds some of the most well known dreadnoughts including the D-18, D-28, and D-45.