The word 'generation' entered English in the early 14th century from Old French 'generacion,' itself from Latin 'generātiōnem,' the accusative of 'generātiō' (a begetting, a producing). The Latin derives from 'generāre' (to beget, to produce), built on 'genus' (birth, origin, race, kind), which descends from the Proto-Indo-European root *ǵenh₁- (to beget, to give birth). This root is one of the most productive in the Indo-European family, spawning vocabulary in virtually every daughter language.
In its earliest English use, 'generation' referred primarily to the act of begetting or producing offspring — a biological process. The Wycliffe Bible (c. 1382) used it in this sense. By the 16th century, the word had extended to mean 'a group of individuals born at the same time,' and by the 17th century, it had acquired the temporal sense of 'the average interval between births in successive degrees of descent' — roughly 25 to 30 years.
The PIE root *ǵenh₁- left an extraordinary legacy. Through Latin 'genus,' it gave English 'genus,' 'genre,' 'gender,' 'generic,' 'generous' (originally meaning 'of noble birth'), 'genial' (having the qualities of one's genius or birth-spirit), 'congenital' (present from birth), 'degenerate' (fallen from one's kind), 'regenerate' (born again), 'ingenious' (inborn talent), and 'gentle' (of good birth — which later softened to mean 'mild'). Through Latin 'gēns' (clan, people), it produced 'nation,' 'gentle,' and 'gentry.'
Through Greek 'génos' (race, kind) and 'génesis' (origin, creation), it gave 'genesis,' 'gene,' 'genetic,' 'genealogy,' 'genocide,' 'eugenics,' 'hydrogen' (water-begetter), and 'oxygen' (acid-begetter). Through the Germanic branch, *ǵenh₁- produced Old English 'cynn' (kin, kind, race), which gave modern English 'kin,' 'kind' (both the noun meaning 'type' and the adjective meaning 'gentle — one who acts according to their nature'), 'kindred,' and 'king' (from *kuningaz, 'son of the kin/people').
Sanskrit 'janas' (people, race) and 'janati' (begets) descend from the same root, as does the name of the Hindu deity Gaṇeśa (lord of the people/hosts). The root even appears in the name 'Eugene' (well-born) and the Latin 'genius' — originally a personal guardian spirit associated with one's birth.
The modern sociological use of 'generation' to label demographic cohorts — the Lost Generation, the Baby Boomers, Generation X, Millennials, Generation Z — emerged in the 20th century, influenced by the sociologist Karl Mannheim's 1928 essay 'The Problem of Generations.' Mannheim argued that a generation is defined not merely by birth years but by shared historical experiences during formative years. This usage has become so dominant that many English speakers no longer think of 'generation' as meaning 'the act of begetting' at all — yet every power plant still 'generates' electricity, and every algorithm still 'generates' output, preserving the original sense of bringing something into being.