In most sheet music books, Cdim or C° denotes a diminished seventh chord with root C. Some modern jazz books and some music theory literature use Cdim or C° to denotes diminished chord, while Cdim7 or C°7 denotes a diminished seventh chord.
A diminished 7th chord is comprised of a diminished triad ( is a triad consisting of two minor thirds above the root) plus a double flattened 7th (same note as the 6th). Its primary use is to lead to the tonic or root note of the song.
Here are a few ways to play a diminished 7th chord.
| Fret | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| Chord | C | C#/Db | D | D#/Eb | E | F | F#/Gb | G | G#/Ab | A | A#/Bb | B |
| Fret | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| Chord | B | C | C#/Db | D | D#/Eb | E | F | F#/Gb | G | G#/Ab | A | A#/Bb |
| Fret | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| Chord | F#/Gb | G | G#/Ab | A | A#/Bb | B | C | C#/Db | D | D#/Eb | E | F |