The chord with a minor third, a lowered (diminished) fifth, and a minor seventh. Formally called 'minor 7 flat 5'. This chord probably evolved from the IV minor 6th chord, which was common in the swing period; if its sixth is taken to be the root, a half-diminished chord results. The symbol is a small O with a diagonal slash. It is most often the harmony of the ii in a ii-V-I progression in a minor key. Two different scales have been commonly used for this chord; one with a flat 9th, the 'locrian', and one with an unflatted ninth, the latter scale being more modern.