I'm not sure of the exact word you are looking for, but the general idea is that the federal law will always reign supreme if there is ever a conflict between the federal and state laws. Federal law is superior or higher-ranking or more preferable, etc.
Here is the exact phrasing from Article VI of the US Constitution: "This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding."