what is diminished in music
2. A diminished chord is the root, the flatted third, and the flatted fifth. So the notes in a C diminished chord are: C, Eb, & Gb. (It is like a C minor, {C, Eb, & G} with the fifth, G, also flatted.) A C diminished chord would typically be denoted either: C dim, C Dim and occasionally as C-. 1  3 Edit step.