Source : Webster's Revised Unabridged Dictionary (1913)

Paranoia \Par`a*noi"a\, n. (Med.)
   A chronic form of insanity characterized by very gradual
   impairment of the intellect, systematized delusion, and
   usually by delusious of persecution or mandatory delusions
   producing homicidal tendency. In its mild form paranoia may
   consist in the well-marked crotchetiness exhibited in persons
   commonly called ``cranks.'' Paranoiacs usually show evidences
   of bodily and nervous degeneration, and many have
   hallucinations, esp. of sight and hearing.

Paranoia \Par`a*noi"a\ (p[a^]r`[.a]*noi"[.a]), n. [NL., fr. Gr.
   para`noia.] (Med.)
   Mental derangement; insanity.

Source : WordNet®

paranoia
     n : a psychological disorder characterized by delusions of
         persecution or grandeur