four-decade

The compound adjective "four-decade" is a modern English formation that transparently combines two established numerical and temporal concepts. The first element, "four," descends from the Proto-Indo-European root kʷetwóres, which gave rise to the number across many Indo-European languages, including Latin quattuor and its Old English descendant fēower. The second element, "decade," originates from the Greek deka (ten), entering English through Latin and French to signify a ten-year period. The compound's logic is purely arithmetic, literally meaning "four ten-year periods," and its formation follows the productive English pattern of combining a number with a unit of time to create a precise durational adjective, such as "two-day" or "five-year."

Structure: four (number) + decade (period of ten years) - four: From Old English fēower, of Proto-Germanic origin; related to Dutch vier and German vier, from an Indo-European root shared by Latin quattuor and Greek tessares. Functions as a numerical quantifier. - decade: From French décade, via Late Latin decas, decad-, from Greek dekas, dekad-, from deka 'ten'. Functions as a noun denoting a specific time period.