a·nom·a·ly

1. Deviation or departure from the normal or common order, form, or rule.
2. 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. Astronomy The angular deviation, as observed from the sun, of a planet from its perihelion.