dead set

US: (ded′ set′ for 1; 2; ded′ set′ for 3)

WordReference Random House Unabridged Dictionary of American English © 2025

dead set  (ded′ set′ for 1; 2;
ded′ set′ for 3), 

1. firmly decided or determined;
   resolved:
   His family was dead set against the marriage.
2. a serious or determined attempt;
   firm effort:
   He made a dead set at winning the championship.
3. Sport [Hunting.] the stiff posture assumed by a hunting dog in indicating the presence and location of game.

• 1840–50, American.

Collins Concise English Dictionary © HarperCollins Publishers::

dead set adverb

1. absolutely: he is dead set against going to this party

noun

1. the motionless position of a dog when pointing with its muzzle towards game

adjective

1. (of a hunting dog) in this position