- (music) A type of tritone in musical composition comprising six semitones. It spans four diatonic scale degrees like a perfect fourth but with an extension of a 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.
Aurally it is impossible to distinguish between an augmented fourth and a diminished fifth. For this reason one would call it a "tritone" in a context such as ear training, but distinguish between an augmented fourth and a diminished fifth when, for example, analysing a score.