anomaly

ANOM'ALY, n. [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.