The Adim chord (diminished): notes A C D#, degrees 1 – ♭3 – ♭5. Guitar shapes: x0121x, 5675xx, x-x-7-8-10-8, x-12-13-14-13-x.
A chord is the root plus degrees above it, most often stacked in thirds. Major and minor differ only in the lower third: a major third (M3) sounds bright, a minor third (m3) sounds sad. Pick a chord and a root to see its degrees and intervals, and its shapes.
m — minor, M — major, P — perfect, A — augmented interval; the number is the degree count. m3 is 3 semitones, M3 is 4, P5 is 7
A Am A5 A7 Am7 Amaj7 Asus2 Asus4 Aadd9 A6 Am6 A9 Adim Adim7 Am7♭5 Aaug