Anomaly
ANOM'ALY, noun [Gr. inequality, equal, similar.]
1. Irregularity; deviation from the common rule; thus oxen, the plural of ox, is an anomaly in grammar, as the regular plural would be oxes.
2. In astronomy, an irregularity in the motion of a planet, whereby it deviates from the aphelion or apogee.
3. In music, a false scale or interval.