What word means to act in a defiant manner towards authority?

The word that means to act in a defiant manner towards authority is "contumacious." This term originates from legal usage, where it is often applied to describe a person who disobeys or rebuffs the authority or commands of a court or other governing body. In a broader context, it conveys a sense of willful disobedience or resistance against established rules or authority figures.

Understanding this word can be particularly useful in contexts that involve law, governance, or discussions about societal norms where authority may be challenged. The other options, while interesting, pertain to different meanings: "calumny" relates to false statements meant to harm someone's reputation; "cavil" means to make petty or unnecessary objections; and "cozen" refers to the act of deceiving or tricking someone, which does not carry the same connotation of defiance as "contumacious."