Skulduggery is dishonest words that are meant to trick people, like your brother's fast-talking that leaves you doing all of his chores and your own, plus giving him your allowance. He's a master of skulduggery.
Skulduggery is an alteration of the Scottish word for "adultery," sculdudrie. Lies, deceit, having a romantic relationship with someone else's spouse? Sounds like skulduggery — or using clever words to take advantage of a situation, or person — is involved. However, skulduggery can have many other goals, from lying to potential customers about what a product can do or telling voters anything they want to hear in order to secure their votes.