augmented fourth

Noun

 * 1)  A 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.

Usage notes
Aurally and while using well temperament or 12-tone equal temperament, 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.

In most other tunings, however, the augmented fourth and diminished fifth are of different sizes.

Translations

 * Finnish: ylinouseva kvartti
 * French:
 * Polish: kwarta zwiększona