The compound adjective 'three-run' is a modern American English formation specific to the lexicon of baseball. Its first element, 'three', descends from the ancient Proto-Indo-European numeral tréyes, which has remained remarkably stable in meaning across millennia into modern English. The second element, 'run', has a complex history originating in Germanic verbs for rapid motion, but in baseball terminology, it crystallized into a noun denoting the act of a player safely circling the bases to score a point. The compound logically and transparently describes a singular play—typically a home run—that immediately results in three runners crossing home plate, thus merging an ancient numeral with a sport-specific specialization of a much older word.

Structure: three (number) + run (score) - three: From Old English þrīe, þrēo, from Proto-Germanic þrīz, from Proto-Indo-European tréyes. Functions as a numerical quantifier. - run: From Middle English runnen, from Old English rinnan, iernan, from Proto-Germanic rinnaną. In this compound, it functions as a noun meaning a point scored in baseball.