An emolument over and above fixed income or salary  

Solution

Perquisite is a benefit or payment received in addition to one's regular salary, often referred to as "perks." The other options are incorrect: Honorarium is a payment given for professional services that are rendered without any expectation of a fixed fee; Sinecure is a position requiring little or no work but giving the holder financial benefit. And "prerogative" is a right or privilege exclusive to an individual or a group.