Source : Webster's Revised Unabridged Dictionary (1913)

Monomania \Mon`o*ma"ni*a\, 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.

   Syn: Insanity; madness; alienation; aberration; derangement;
        mania. See {Insanity}.

Source : WordNet®

monomania
     n : a mania restricted to one thing or idea [syn: {possession}]