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.
Unpredictable, erratic or fickle; mercurial.
The metal mercury.
An amalgam of mercury and tin applied to the backs of mirrors, quicksilvering.
To overlay with quicksilver.
To treat with quicksilver.