century

The word 'century' entered English in the late fourteenth century from Latin 'centuria,' meaning 'a group of one hundred.' The Latin word derives from 'centum' (hundred), from PIE *ḱm̥tóm.‌​‌​‍​‍​‍​‌​‍​‍​‌​‍​‌​‌​‌​‌​‌​‌​‌​‍​‍​‌​‌​‌​‌​‍​‍​‍​‍​‌​‌​‍​‌​‍ In Roman usage, 'centuria' had two primary meanings: a unit of the Roman army (nominally one hundred soldiers, commanded by a centurion) and a voting unit in the Roman Republic's comitia centuriata (the centuriate assembly). The temporal meaning — a hundred years — developed later and became standard in English only in the seventeenth century.

The Roman century was the backbone of the Roman military machine. The legion (typically 5,000-6,000 men) was divided into cohorts, and each cohort was divided into centuries. Despite the name, a century in the imperial period usually contained about eighty fighting men plus support personnel. The centurion — the officer commanding a century — was the professional core of the Roman army, a career soldier who had risen through the ranks. The centurion's vine-staff (vitis) was the symbol of his authority and his readiness to use corporal punishment.

The word's shift from 'a group of a hundred' to 'a hundred years' happened gradually. Latin used 'saeculum' (age, generation, century) for the temporal sense, and the Romance languages followed: French 'siècle,' Italian 'secolo,' Spanish 'siglo' all derive from 'saeculum,' not from 'centuria.' English went a different way, repurposing 'century' from a spatial/military group to a temporal span. German also chose the 'hundred' route, calquing the concept as 'Jahrhundert' (hundred-year).

The word family from Latin 'centum' includes: 'centurion' (commander of a century), 'centennial' (hundredth anniversary), 'cent' (one hundredth of a dollar), 'percent' (per hundred), 'centimeter' (one hundredth of a meter), 'centigrade' (hundred degrees — the original name for the Celsius scale, which has one hundred degrees between the freezing and boiling points of water), 'centipede' (hundred-footed arthropod, though actual leg counts range from 30 to 354, never exactly one hundred), and 'centenary' (a hundredth anniversary, more common in British English than 'centennial').

In cricket, a 'century' is a batsman's score of one hundred or more runs in a single innings — a significant achievement celebrated in the sport's culture. Don Bradman's Test batting average of 99.94 means he averaged just under a century per innings across his career, a record that remains unmatched.

The concept of the century as a historical unit has profoundly shaped how we periodize and narrate the past. 'The nineteenth century,' 'the twentieth century' — these labels imply that meaningful cultural or historical change aligns with the arbitrary mathematical boundaries of hundred-year periods. Historians have long debated whether this is true. Eric Hobsbawm proposed 'the long nineteenth century' (1789-1914) and 'the short twentieth century' (1914-1991), arguing that meaningful historical periods do not respect calendrical boundaries. The century is a convenient but imperfect unit of historical organization — a round number imposed on the continuous flow of events.

The PIE root *ḱm̥tóm (hundred) remains visible in 'century,' connecting modern English speakers to the numeral system of the proto-language. Every time we say 'the twenty-first century,' we invoke a word that descends from the same root that Proto-Indo-European speakers used to count their cattle on the steppe, five or six thousand years ago.