Extremely weary; utterly exhausted. Also 'dead tired' or 'dog tired.'
Examples:
- Mom was in the kitchen all day and was dead on her feet.
- I'd love to go, but I'm dead tired.
Origin: Use of dead for 'exhausted' dates from early 1800s; 'dead on one's feet' from late 1800s.
Synonyms: dead tired, dog tired