Wordnet 3.0
ADJECTIVE (1)
1. 
 characterized by or constituting an obsession; 
- Example: "the obsessional character of his response"- Example: "obsessive gambling"[syn: obsessional, obsessive]
The Collaborative International Dictionary of English v.0.48:
obsessional \obsessional\ obsessive \obsessive\adj.
   Persistently and abnormally preoccupied with some
   unreasonable idea.
   Syn: compulsive.
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
obsessional
    adj 1: characterized by or constituting an obsession; "the
           obsessional character of his response"; "obsessive
           gambling" [syn: obsessional, obsessive]