A minor major seventh is the chord you get when you take a minor triad
and add to it the seventh note of the major scale
. They're notated Cm-maj7
or in jazz
For example, an A minor triad is A C E. The seventh note of the A major scale is G#, so the Am-maj7 chord consists of A C E G#.
Rather a harsh-sounding chord, owing to the augmented triad and semitone dissonance it contains.
Compare with the major seventh, minor seventh and dominant seventh chords.