A chronic form of insanity marked by systematized delusion is a ___.

The term that describes a chronic form of insanity characterized by systematized delusion is "paranoia." This word refers specifically to a mental condition where an individual holds strong, persistent, and often irrational beliefs that others are plotting against them or that they are being persecuted. The correct usage of the term in this context is crucial, as it reflects the established terminology in psychology and psychiatry.

In this question, selecting "paranoid" does not accurately capture the definition provided. "Paranoid" is generally an adjective used to describe someone exhibiting signs or symptoms of paranoia, but it does not represent the condition itself. In contrast, "paranoia" is the noun that directly refers to the mental health disorder, making it the appropriate answer to the question posed.