1. a paranoid state.

2. a former diagnosis for a relatively rare disorder, distinct from paranoid schizophrenia, in which the person reasons rightly from a wrong premise and develops a persistent, well-systematized, and logically constructed set of persecutory delusions, such as being conspired against, poisoned, or maligned. It is equivalent to persecutory-type delusional disorder.

3. historically, any psychiatric disorder characterized by persistent delusions. See also classical paranoia.

4. in ancient times, any mental disorder or delirium. —paranoiac n., adj.