Diminished interval.

A perfect or minor Interval from which a chromatic semitone has been subtracted. The perfect 5th C–G is made into a diminished 5th by raising C or lowering G (i.e. C–G or C–G). The diminished 3rd (e.g. F–A) is the inversion of the augmented 6th. A doubly diminished interval is made by subtracting two chromatic semitones from a perfect or minor interval, for example G–F, G–F and G-F are all doubly diminished 7ths derived from the minor 7th G–F.