A doubtful person or thing.
Experiencing or showing doubt, sceptical.
Subject to, or causing doubt.
Improbable or unlikely.
Unclear or unreliable.
Suspicious, or of dubious character.
Undecided or of uncertain outcome.
The act of making a promise.
Showing promise, and likely to develop in a desirable fashion.
a promising young apprentice
Encouraging and inspiring confidence.