A relatively rare type of chord in music. It consists of a root tone, the note a minor third above it, and the note a minor third above the second note. It is also the same as a minor chord with the fifth lowered a half-step. Notated by appending a "°" (little circle, degree sign, "Cheerio") to the root tone (e.g., the C diminished chord would be represented as C°) or by other rarer ways (Cdim, Co).

The notes included in the diminished chord for each note:

Cb°  |Cb  Ebb Gbb
C°   |C   Eb  Gb
C#°  |C#  E   G
Db°  |Db  Fb  Abb
D°   |D   F   Ab
D#°  |D#  F#  A
Eb°  |Eb  Gb  Bbb
E°   |E   G   Bb
E#°  |E#  G#  B
Fb°  |Fb  Abb Cbb
F°   |F   Ab  Cb
F#°  |F#  A   C
Gb°  |Gb  Bbb Dbb
G°   |G   Bb  Db
G#°  |G#  B   D
Ab°  |Ab  Cb  Ebb
A°   |A   C    Eb
A#°  |A#  C#  E
Bb°  |Bb  Db  Fb
B°   |B   D   F
B#°  |B#  D#  F#
(where bb = double flat, b = flat, and # = sharp.)

Of course, any of these chords can be inverted, or spelled out in a different order. The root position of an diminished chord uses the first tone first, the first inversion uses the second tone first, and the second inversion uses the third tone first. For example, the root position of the B diminished chord can be spelled B-D-F, the first inversion can be spelled D-F-B, and the second inversion can be spelled F-B-D.

Some chords created by adding tones to the diminished chord are the fully-diminished seventh chord, half-diminished seventh chord, or diminished major seventh chord. Notice that some variants of the augmented chord are notated not by putting a "°" right after the root tone, but by notating the related minor chord and then appending a "b5" (meaning, the fifth is lowered a half-step). For example, C minor major seventh is notated CmM7; therefore, C dimished major seventh is notated CmM7b5.

cf. major chord, minor chord, augmented chord

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