Noun
augmented fourth (plural augmented fourths)
(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.
You knew exactly who the good guys were and who were the bad guys just by the chord: the good guys got a perfect fifth - strong, compassionate - the bad guys got an augmented fourth... Just a semitone, but sometimes in life when you make the wrong choices, it's just a semitone out. Bill Bailey