The term 'ten-gallon hat' is an American English invention from the late 19th or early 20th century, associated with the cowboy culture of the American West. Its etymology is not literal but likely folkloric; the 'gallon' here does not refer to the hat's liquid capacity. One prominent theory suggests it derives from a Anglicization of the Spanish term 'galón', meaning 'braid' or 'galloon' (a decorative trim), referring to the hat's decorative band. Another theory posits it as a hyperbolic exaggeration, humorously implying the hat was so large it could hold ten gallons. The modern meaning has completely detached from volumetric measurement, solidifying as a descriptor for a specific, iconic style of wide-brimmed, high-crowned headwear.

Structure: ten (number) + gallon (unit of capacity) 'Ten' originates from Old English 'tīen', from Proto-Germanic 'tehun', from Proto-Indo-European 'déḱm̥', functioning as a numeral. 'Gallon' originates from Old Northern French 'galon', a liquid measure, likely of Celtic origin, functioning as a noun for a unit of volume.