dead set against (someone or something)

Completely opposed to someone or something. Most of the department is dead set against one of our peers becoming our boss, even temporarily. Many people in our small town are dead set against that big construction project, and I think you'll have a hard time changing their minds.

totally opposed to someone or something. I'm dead set against the new tax proposal. Everyone is dead set against the mayor.

Completely opposed to, as in His parents were dead set against John's taking a year off from college. Set against has been used to mean "opposed to" since the 1400s. Dead acquired the meaning "utterly" in the 16th century.

Unutterably opposed. This Americanism probably comes from industry, where a machine is said to be dead set when it is fastened so that it cannot be made to move. The transfer to firm resolve or hostility against some person, course of action, and so on, was made by the early nineteenth century. “A dead set is to be made from various quarters against the abominable innovation of publishing Divisions by authority” (General P. Thompson, 1836).