The Etymology of Fatigue
Fatigue is a Latin loanword that has migrated quietly from the body to the bridge. The Latin verb fatīgāre meant to wear out, to weary, to exhaust, and its internal etymology is uncertain — some lexicographers tentatively reconstruct a Proto-Indo-European root *bhēd- (to lash, beat), but the proposal is not firm. French fatiguer continued the sense unchanged, and the action noun fatigue named the resulting condition of weariness. English took fatigue from French in the early 17th century, originally describing physical or mental tiredness. The military used it from the 18th century for non-combat duties (camp fatigue, fatigue dress) and for the rough work-clothes worn during them — hence American fatigues for military uniforms. The most consequential modern extension came from 19th-century engineering: investigators studying repeated railway-axle and bridge failures discovered that metals can crack and fail under repeated cyclic stress well below their static strength, and they named this phenomenon fatigue by analogy with bodies tired by repeated exertion.