Webster’s Revised Unabridged Dictionary · 1913
Monomania
Mon′o·ma′ni·a (mŏn′ō·mā′nĭ·ȧ), 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.