Unclear or unreliable.
Experiencing or showing doubt, sceptical.
Subject to, or causing doubt.
Improbable or unlikely.
Suspicious, or of dubious character.
Undecided or of uncertain outcome.
A doubtful person or thing.
Not elaborated upon, or not accompanied by restrictions or qualification; undescribed.
Outright; thorough; utter.
Not qualified, ineligible, unfit for a position or task.