early 15c., from grand (adj.) + father (n.), probably on analogy of French grand-père. Replaced grandsire and Old English ealdefæder. Grandfather clause originally (1900) referred to exemptions from post-Reconstruction voting restrictions in the U.S. South for men whose forebears had voted before the Civil War. Grandfather clock is c.1880, from the popular song; they were previously known as tall case clocks or eight-day clocks.