fatigue

The Latin verb fatigare meant to drive to weariness, to exhaust by pressing without pause. Roman writers used it for the physical collapse that comes after sustained labor: the tired slave, the spent legionary, the horse run too long. Fatigare likely combined an old root for fullness or sufficiency with agere, to drive or act, making the sense something like to drive past the point of bearing. The word described not weakness but overuse.

Old French received the verb as fatiguer by the twelfth century, and by the seventeenth century the French army had given the noun fatigue a specific military meaning: the physical labor that soldiers performed outside of combat, the digging of trenches, the hauling of supplies, the endless maintenance of camps. This was not rest and not battle but the grinding work in between. The French used fatigue to name not the exhaustion of fighting but the exhaustion of the work that made fighting possible.

English borrowed fatigue around 1690, first in this military sense. By 1719, Alexander Pope used it in a non-military context, describing the tiredness of thought. The medical profession adopted it in the eighteenth century to describe a specific physiological state: the reduced capacity for response that follows prolonged stimulation of a nerve or muscle. This was a precise clinical observation dressed in a borrowed French noun.

Materials science adopted fatigue in the nineteenth century with an entirely new precision. Engineers studying metal failures in railway axles and bridges found that metal could crack and fail under repeated stress well below the force required to break it in a single blow. They called this metal fatigue, and the concept transformed structural engineering. The word had traveled from the human body to the body of a bridge, carrying the same essential meaning: the cost of repetition.