The compound adjective 'years-long' is a modern English formation following a productive pattern for creating duration-based descriptors. It combines the plural noun 'years', which traces back to the Proto-Germanic 'jēram' meaning "year," with the adjective 'long', from Proto-Germanic 'langaz' meaning "having great linear extent or duration." This pattern logically and transparently conveys an extended timespan, directly linking the measurable unit ("years") with the quality of extension ("long"). Its construction mirrors similar compounds like 'hours-long' or 'decades-long', illustrating a straightforward method in English for specifying the duration of states or events.

Structure: years (noun) + long (adjective) - years: From Old English 'gear', of Germanic origin; related to Dutch 'jaar' and German 'Jahr'. Functions as a plural noun indicating a period of time. - long: From Old English 'lang', of Germanic origin; related to Dutch 'lang' and German 'lang'. Functions as an adjective describing duration.