1. An action that generates harm to others; deliberate infliction of pain or suffering: The viciousness of the assault by the thugs on the street caused terror to spread throughout the neighborhood.
2. A trait of extreme cruelty: Using his spurs mercilessly on his horse was an act of viciousness by Jack, the rider.
3. Given to immorality, depravity, and extreme harshness or savagery: By day the businessman appeared to be an upright citizen; by night he was committing viciousness against prostitutes.