The word 'windmill' is a transparent compound from two ancient roots. 'Wind' originates from the Proto-Indo-European h₂wéh₁n̥ts, which evolved into the pervasive Germanic term for moving air. 'Mill' traces back to the Latin mola, meaning a millstone or grinding apparatus, which entered Old English via Late Latin. The compound logically names the machine by its power source and its primary function. While early windmills were literally mills powered by wind for grinding, the term's logic seamlessly extended to modern structures that harness wind for other purposes like electricity generation, preserving the core concept of a 'wind-powered machine'.

Structure: wind (air in motion) + mill (grinding machine) - wind: From Old English wind, of Germanic origin; related to Dutch wind and German Wind, from an Indo-European root shared by Latin ventus. The functional role is a noun used attributively to specify the power source. - mill: From Old English mylen, based on Late Latin molinum, from Latin mola 'grindstone, mill'. The functional role is the core noun denoting the machine or structure that performs a specific function (grinding, pumping, or generating power).