Unpredictable, erratic or fickle; mercurial.
To overlay with quicksilver.
To treat with quicksilver.
The metal mercury.
An amalgam of mercury and tin applied to the backs of mirrors, quicksilvering.
Secret; surreptitious.
Done by moving the hand (and arm) from below.
Sly, dishonest, corrupt, cheating.
Insincere; sarcastic.
An underhanded compliment is actually criticism.
His underhanded trick backfired and he was disqualified.
Understaffed.
Devious people, collectively.
In an underhanded manner.