Definition of double flat in US English:

noun

• 1A sign placed before a musical note to indicate that it is to be lowered two semitones.

  Example sentences

  • ‘The sharp raises the note before which it is placed by one semitone; the flat lowers it by one semitone; the double sharp and double flat respectively raise and lower it by a whole tone; the natural cancels any other accidental.’

  1. 1.1 A musical note marked by a double flat or lowered two semitones.
     Example sentences

     • ‘Gurney knows it well - witness the opening line of ‘Sleep’ (D flat-F; D flat-B double flat).’