Real Dictionary

paranoia
uncountable noun: If you say that someone suffers from paranoia, you think that they are too suspicious and afraid of other people.
uncountable noun: In psychology, paranoia is when someone wrongly believes that other people are trying to harm them, or when they believe themselves to be much more important than they really are.

paranoia in American English
a mental disorder characterized by systematized delusions, as of grandeur or, esp., persecution, often, except in a schizophrenic state, with an otherwise relatively intact personality
noun: a disorder characterized by systematized delusions and the projection of personal conflicts, which are ascribed to the supposed hostility of others, sometimes progressing to disturbances of consciousness and aggressive acts believed to be performed in sel

paranoia in British English
noun: a form of schizophrenia characterized by a slowly progressive deterioration of the personality, involving delusions and often hallucinations