The compound adjective "three-mile" is a straightforward combination of the Old English numeral "three" and the unit "mile," which entered English via Latin. "Three" descends from the Proto-Indo-European root trei-, a fundamental numeral that gave rise to equivalents across Indo-European languages. "Mile" originates from the Roman mīlia passuum, meaning "a thousand paces," a standardized measure of distance. The modern compound logically and literally denotes an attribute pertaining to this specific distance, commonly used to define limits, zones, or races, such as a "three-mile limit" or a "three-mile run."

Structure: three (number) + mile (unit of distance) - three: From Old English þrīe, þrēo, from Proto-Germanic þrīz, from Proto-Indo-European tréyes. Functions as a cardinal number. - mile: From Old English mīl, from Latin mīlia (passuum), meaning "thousands (of paces)". Functions as a noun denoting a unit of linear measurement.