1.NounA type of tritone in musical composition. It spans four diatonic scale degrees like a perfect fourth but with an extension of a chromatic semitone. The number of diatonic degrees it spans is what distinguishes it from a diminished fifth.
"e.g. C - F is a perfect fourth, C - F# is an augmented fourth, and C - F♭ is a diminished fourth.; An augmented fourth on C:1" srcset="//upload.wikimedia.org/score/c/i/ci9uoxrc6a7frbwljop80jeb2advg7q/ci9uoxrc.svg 1x" />Audio playback is not supported in your browser. You can download the audio file."