Extremely tired. This graphic hyperbole, with its use of “dead” in the meaning of “utterly fatigued,” is probably related to dead tired, where “dead” means “very” or “absolutely.” This locution has been traced to Irish speech and appears in such clichés as dead wrong for “completely mistaken,” dead right for “absolutely correct,” dead certain for “totally sure,” and others. “Dead on one’s feet” became common in the mid-twentieth century. John Braine used it in Life at the Top (1962): “Honestly, I’m dead on my feet.”