Inflected forms: pl. a·nom·a·lies 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.