noun

• (countable) A devious device or trick.
  "A private company cannot get away with a skulduggery of that sort. Once it has paid out its money for taxes, it cannot reach into the public treasury and get it back and apply it on its amortization account."
• (uncountable) Dishonest, underhanded, or unscrupulous activities or behaviour.
  "And I have another reason which I will express to my St Paul friends, and that is, that they have always been controlled in their political action here by a class of men who have always some traps set for the country members—by men who are always up to this border ruffian kind of trickery—this kind of skullduggery, as it is called in Minnesota. And now St. Paul allows herself to be controlled by these same border ruffian politicians."