the GNU version of the Collaborative International Dictionary of English
adj. Persistently and abnormally preoccupied with some unreasonable idea.
The Century Dictionary and Cyclopedia
Of or pertaining to a siege; obsidional.
Pertaining to or of the nature of obsession.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. characterized by or constituting an obsession
Word Usage
"Freud has delimited what he calls obsessional or compulsion neurosis (Zwangsneurosis), which is classed under psychasthenia by the French and under neurasthenia by others."