Webster’s Revised Unabridged Dictionary · 1913
Obsession
Ob·ses′sion (ŏb·sĕsh′ŭn), n. [L. obsessio: cf.F. obsession.] 1. The act of besieging. Johnson.
2. The state of being besieged; — used specifically of a person beset by a spirit from without. Tylor.
Whether by obsession or possession, I will not determine. Burton.