Fatigue is a feeling of extreme physical or mental tiredness.

You can say that people are suffering from a particular kind of fatigue when they have been doing something for a long time and feel they can no longer continue to do it.

Fatigues are clothes that soldiers wear when they are fighting or when they are doing routine jobs.

Fatigue in metal or wood is a weakness in it that is caused by repeated stress. Fatigue can cause the metal or wood to break.