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.
That cannot be investigated or searched into; unknowable, inscrutable.
Not capable of being searched; on which one cannot perform a search.
That cannot be sought out or looked for.