Monomania
Pronunciation : Mon`o*ma"ni*a
Part of Speech : n.
Etymology : [Mono- + mania.]
Definition : Defn: 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.
Syn. -- Insanity; madness; alienation; aberration; derangement; mania. See Insanity.
Source : Webster's Unabridged Dictionary, 1913