1. An extreme, irrational, and unreasonable suspicion or distrust of other people and their motives.
2. A psychiatric disorder characterized by an elaborate, overly suspicious system of thinking which often includes delusions of persecution and grandeur usually centered on one major theme; such as, a financial matter, a job situation, an unfaithful spouse, or another problem including being followed or monitored by a governmental intelligence agency; by outer space aliens; being the victim of computer tampering; or of being poisoned.
3. A condition in which patients show persistent persecutory delusions or delusional jealousy, with emotion and behavior appropriate to the content of the delusional system. 4. Etymology: "mental disorder characterized by systematized delusions", 1891 (earlier paranoea 1811), from Greek paranoia, "mental derangement, madness,"; which came from paranoos, "mentally ill, insane", from para-, "beside, beyond" + noos, "mind" and Greek noein, "to think".