The Collaborative International Dictionary
anharmonic function
Anharmonic \An`har*mon"ic\, a. [F. anharmonique, fr. Gr. 'an priv. + ? harmonic.] (Math.) Not harmonic.
The anharmonic function or anharmonic ratio of four points abcd on a straight line is the quantity (ac/ad):(bc/bd), where the segments are to be regarded as plus or minus, according to the order of the letters.