Which word best describes behavior that is cunningly deceitful?

The term "Machiavellian" best describes behavior that is cunningly deceitful. This word originates from the political philosophy of Niccolò Machiavelli, particularly as outlined in his work "The Prince." It refers to the employment of deceit and manipulation in the pursuit of power and personal gain, often disregarding morality and ethics. In contemporary usage, someone described as Machiavellian may use clever and unscrupulous tactics to achieve their goals, which aligns perfectly with the concept of being cunningly deceitful.

Other choices do not convey the same meaning. Invective refers to harsh or abusive language, which lacks the nuance of cunning deceit. Laconic describes a style of speaking that is brief and concise, and does not imply deceitfulness at all. Lassitude indicates a state of physical or mental weariness, which is unrelated to deceitful behavior. Therefore, Machiavellian is the most fitting term among the options provided.