Meaning of ACCIDENTAL in English

ACCIDENTAL

in music, sign placed immediately to the left of a note to show that the note must be changed in pitch. A sharp () raises a note by a semitone; a flat () lowers it by a semitone; a natural () restores it to the original pitch. Double sharps () and double flats () indicate that the note is raised or lowered by two semitones. A single natural cancels a double sharp or flat; a natural next to a sharp or flat (as ) cancels half of a double sharp or flat. Sharps or flats that are placed at the beginning of a musical staff indicate the tonality, or key, of the music and are not considered accidentals. Accidentals were first applied to the note B, by about the 10th century. To fulfill certain theoretical and aesthetic rules, B was sometimes flatted and, later, F was sometimes sharped. At first there was no sign for a natural; a sharp (written or ) cancelled a flat, a flat cancelled a sharp. By the late Renaissance, E, A, and C were fairly common. Accidentals applied to all notes became increasingly common in music of subsequent periods.

Britannica English vocabulary.      Английский словарь Британика.