General terms:
* Evil
* Depravity
* Sinfulness
* Corruption
* Immorality
* Iniquity
* Vice
* Malice
* Perversity
* Atrocity
* Cruelty
More specific terms:
* Villainy: implies deliberate and calculated wickedness, often associated with a villain.
* Heinousness: emphasizes the extreme gravity and repulsiveness of the wickedness.
* Abomination: suggests something that is deeply offensive and morally reprehensible.
* Vileness: emphasizes the low and base nature of the wickedness.
* Cunning: implies that the wickedness is achieved through cleverness and deception.
Informal terms:
* Badness: a simple and straightforward way to describe wickedness.
* Evilness: a slightly more informal way to describe wickedness.
The best synonym for "wickedness" will depend on the specific context of your writing.