Nepotistic is the adjective for nepotism: a nepotistic hire, a nepotistic system, nepotistic behaviour. It describes the kind of act or the kind of workplace, rather than naming the practice itself. It is a formal, often critical word — you will see it in news and essays more than in casual talk. If a company always promotes the owner’s children, people may call the culture nepotistic. Same idea as nepotism, but used to paint a picture of how something is done, not to name the habit as a thing.