anomaly (n.)

1570s, "unevenness;" 1660s, "deviation from the common rule," from Latin anomalia, from Greek anomalia "inequality," abstract noun from anomalos "uneven, irregular," from an- "not" (see an- (1)) + homalos "even," from homos "same," from PIE root *sem- (1) "one; as one, together with." From 1722 as "something abnormal or irregular."