anomaly

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Deviation or departure from the normal or common order, form, or rule.
2. n. One that is peculiar, irregular, abnormal, or difficult to classify: "Both men are anomalies: they have . . . likable personalities but each has made his reputation as a heavy” ( David Pauly).
3. n. Astronomy The angular deviation, as observed from the sun, of a planet from its perihelion.

Century Dictionary and Cyclopedia

1. n. Deviation from the common rule or analogy; something abnormal or irregular.
2. n. In astronomy, an angular quantity defining the position of a point in a planetary orbit, taken to increase in the direction of planetary motion. In ancient astronomy it was reckoned from apogee; in early modern astronomy, from aphelion, except in cometary orbits; but since Gauss, from perihelion.
3. n. In music, a small deviation from a perfect interval in tuning instruments with fixed notes; a temperament.
4. n. In mod. astron., the angle at the sun between perihelion and the place of a planet.
5. n. In meteorology, the amount by which a given observed quantity is greater or less than an assumed ideal or normal value; a departure.

Wiktionary

1. n. A deviation from a rule or from what is regarded as normal.
2. n. Something or someone that is strange or unusual.
3. n. sciences Any event or measurement that is out of the ordinary regardless of whether it is exceptional or not.
4. n. astronomy Any of various angular distances.
5. n. biology A defect or malformation.
6. n. quantum mechanics A failure of a classical symmetry due to quantum corrections.
7. n. dated An irregularity or disproportion.

GNU Webster's 1913

1. n. Deviation from the common rule; an irregularity; anything anomalous.
2. n. The angular distance of a planet from its perihelion, as seen from the sun. This is the true anomaly. The eccentric anomaly is a corresponding angle at the center of the elliptic orbit of the planet. The mean anomaly is what the anomaly would be if the planet's angular motion were uniform.
3. n. The angle measuring apparent irregularities in the motion of a planet.
4. n. (Nat. Hist.) Any deviation from the essential characteristics of a specific type.

WordNet 3.0

1. n. (astronomy) position of a planet as defined by its angular distance from its perihelion (as observed from the sun)
2. n. deviation from the normal or common order or form or rule
3. n. a person who is unusual