WordWeb Online

1. Fraught with uncertainty or doubt
   "dubious about agreeing to go";
   - doubtful
    
2. Open to doubt or suspicion
   "he has a dubious record indeed"; "what one found uncertain the other found dubious or downright false";
   - doubtful, dubitable, in question, doubtable, questionable
    
3. Not convinced
   "they admitted the force of my argument but remained dubious"

See also: deniable, incertain [non-standard], questionable, uncertain, unconvinced, unsure

Encyclopedia: Dubious