diminished fourth
musical interval produced by narrowing a perfect fourth by a chromatic semitone (e.g. from C♯ to F or from C to F♭); enharmonically equivalent to a major third
en-GB/dɪˈmɪnɪʃt ˈfɔːθ/
en-US/dɪˈmɪnɪʃt ˈfɔɹθ/
musical interval produced by narrowing a perfect fourth by a chromatic semitone (e.g. from C♯ to F or from C to F♭); enharmonically equivalent to a major third