Enharmonic

Enharmonic 

(1) A term that refers to tones that are the same degree of the chromatic scale but are named and written differently (for example, F sharp and G flat), to intervals consisting of the same tones but “spelled” differently (for example, major sixth and diminished seventh), to chords that are tonally but not harmonically equivalent (for example, a diminished seventh chord in which 1–3 notes undergo an enharmonic substitution becomes one of the inversions of the other diminished seventh chords), or to keys that are tonally but not harmonically equivalent (F sharp major and G flat major). The concept of enharmonic tones came about as a result of equal temperament, in which the octave is divided into 12 equal semitones; it allows the composer to make use of enharmonic modulation, a change of key made by altering enharmonically one or two notes of a chord, thereby changing the chord’s harmonic meaning and inducing a different progression.

(2) One of the ancient Greek scale forms, a tonality that included intervals of approximately a quarter tone.