piano chord
C♯dim7
C♯1E♭3G♭5B♭♭♭7
Three minor thirds stacked. The seventh is doubly diminished, which is why it is written with a double flat.
Written the other way round it is D♭dim7 — the same twelve keys on a piano, a different piece of notation.
What is true of it
C♯dim7 is C♯, E, G and B♭ — 1, b3, b5 and bb7 counted from C♯.