If someone is described as 'Machiavellian' this means that they are scheming and manipulative. The word is often applied to those who are in positions of authority and who seek to maintain a stranglehold on power in cunning ways. The term is derived from the Rennaissance political writer Niccolo Machiavelli, who wrote a famous political treatise, The Prince (1532) outlining the principles and practices of state power.
In Measure for Measure, the Duke of Vienna leaves his deputy Angelo in charge of the city and Angelo proves himself to be a strict and also devious ruler. He maintains an appearance of outward virtue but behind the scenes he plays false to his own publicly-proclaimed ideal of sexual purity when he demands that Isabella sleep with him in order to save the life of her brother Claudio. Thus, in true Machiavellian style, Angelo says one thing and does another, while keeping a strict rule over others.