Chromatic

Chromatic, in Music (from the name of one of the Greek tetrachords or scales), is applied to notes in a melodic progression which are raised or lowered by accidentals, without changing the key of the passage, and also to chords in which such notes occur. The chromatic scale is one proceeding by semitones alone. Much irregularity prevails in the method of writing such progressions. The most strictly correct practice is to write only such chromatic notes as could occur in chords belonging to the key in which the passage is written.