There's a lesson somewhere in the BGU Blog on the Peter Green song "Need Your Love So Bad" which has a diminished chord in it - maybe Griff explains the chord in that lesson, I don't remember.
Apropos your question - Be aware - my understanding is that the Diminished chord and the Diminished 7th chord are exactly the same thing - a Tonic (Root), Flat 3rd, Flat 5th, double-flat 7th. In C that's C, Eb, Gb, Bbb (which is the same as A).
Do Not mistake that for the "half-diminished" or Minor 7th Flat 5 chord, which is a Tonic (Root), Flat 3rd, Flat 5th, Flat 7th. In C, that's C, Eb, Gb, Bb.
The half-diminished has a Flat 7th, while the (full) diminished has a double-flat 7th (enharmonic of the 6th).