fatigue

This term describes a deep, systemic exhaustion that goes beyond simple sleepiness. It suggests a depletion of reserves where the body or mind can no longer function at full capacity, often carrying a clinical or heavy tone compared to the casual word tired. In engineering and materials science, the word takes on a technical meaning referring to the weakening of a material caused by repeated stress. This creates a mental image of microscopic cracks forming over time until a sudden, catastrophic failure occurs.