double sharp
Noun
Meaning
a musical notation of two sharps in front of a note indicating that it is to be raised by two semitones
Source: WordNetAlternative names
Double-sharp
Synonyms
Hypernyms
Examples
Adding a double accidental (double sharp) to F in this case only raisees F by one further semitone, creating G natural.
Conversely, adding a double sharp to any other note not sharped or flatted in the key signature raises the note by two semitones with respect to the chromatic scale.
For example, in the aforementioned key signature, any note that is not F, C, G, and D is raised by two semitones instead of one, so an A double sharp raises the note A natural to the enharmonic equivalent of B natural.
Likewise (and more commonly), a double sharp double sharp sign on a key signature with a single sharp indicates only a double sharp, not a triple sharp.