A diminished chord
A diminished guitar chord is also written as Adim or Ao or Am♭5.
Guitar chords chart for A diminished chord with suggested finger positions on the guitar fretboard is shown below.
View diminished chord for guitar with other root notes
C - D - E - F - G - A - B - C♯ - D♯ - F♯ - G♯ - A♯ - D♭ - E♭ - G♭ - A♭ - B♭