interval
D major seventh
DlowerC♯upperM711 half steps
Eleven half steps: a half step short of the octave, which is why it leans on it.
On the keyboard
What is true of it
D up a major seventh is C♯: 11 half steps, and 7 letters counting both ends.
Turn it upside down — put the D on top — and it becomes a minor second. The two numbers always add to nine, and the two sizes to twelve.
It is a dissonance.
Every interval on D
D → E♭minor second · dissonanceD → Emajor second · dissonanceD → Fminor third · imperfect consonanceD → F♯major third · imperfect consonanceD → Gperfect fourth · perfect consonanceD → G♯augmented fourth · dissonanceD → A♭diminished fifth · dissonanceD → Aperfect fifth · perfect consonanceD → B♭minor sixth · imperfect consonanceD → Bmajor sixth · imperfect consonanceD → Cminor seventh · dissonance