C# Diminished (C#dim)
Also written as Db Diminished (Db and C# are the same key).
1+b3+b5
Notes in C# Diminished
C# (root)EG
Inversions
Same notes as C# Diminished, with a different chord tone as the lowest note. Useful for smoother movement between chords instead of jumping around the keyboard.
Root position
C# in the bass
1st inversion
E in the bass
2nd inversion
G in the bass
Play C#, E and G together and you get C# Diminished.
Stack two minor thirds and the fifth shrinks along with the third, producing a triad that never feels at rest. Diminished chords are unstable by design, built to lean somewhere else, usually resolving up by a half step. Played alone it can sound almost comical, but tucked between two other chords it's one of the most useful tension devices in tonal music.