What is the meaning of dubious?

adjective

• Fraught with uncertainty or doubt.
  • usage: "they were doubtful that the cord would hold"; "it was doubtful whether she would be admitted"; "dubious about agreeing to go"
  • synonyms: doubtful
• Open to doubt or suspicion."the candidate's doubtful past"; "he has a dubious record indeed"; "what one found uncertain the other found dubious or downright false"; "it was more than dubitable whether the friend was as influential as she thought- Karen Horney
  • synonyms: doubtful, dubitable, in question
• Not convinced.
  • usage: "they admitted the force of my argument but remained dubious"