n. [ Demon + mania. ] A form of madness in which the patient conceives himself possessed of devils. [ 1913 Webster ]
n. [ Mono- + mania. ] Derangement of the mind in regard of a single subject only; also, such a concentration of interest upon one particular subject or train of ideas to show mental derangement. [ 1913 Webster ]
n. A person affected by monomania. [ 1913 Webster ]