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.
Artful, tricky or cunning.
Sharp, snithy, piercing.
Showing clever resourcefulness in practical matters.
Streetwise, street-smart.
Knowledgeable, intelligent, keen.
Nigh accurate.
Severe, intense, hard.