Definition of New Oxford American Dictionary: par·a·noi·a /,parә’noiә/,pɛrә’nɔɪә/ ▶n. a mental condition characterized by delusions of persecution, unwarranted jealousy, or exaggerated self-importance, typically elaborated into an organized system. It may be an aspect of chronic personality disorder, of drug abuse, or of a serious condition such as schizophrenia in which the person loses touch with [...]