The term 'yard-long' is a transparent English compound, formed by directly combining two native Germanic elements. The first element, 'yard', originates from the Old English word for a rod or stick, which evolved into a standard unit of linear measurement. The second element, 'long', is one of the most fundamental adjectives in the language, describing linear extent. When combined, they create a precise descriptive term, literally "as long as a yard." This logical construction was first applied as a straightforward measurement adjective. Later, it was adopted as the common name for the asparagus bean (Vigna unguiculata subsp. sesquipedalis), a legume whose pods are notably characterized by their potential to reach this specific length, thus providing a vivid and memorable folk name based on a salient physical attribute.

Structure: yard (unit of length) + long (having length) yard: From Old English gierd, gyrd (rod, stick, measure of length). Of Germanic origin; related to Dutch gard and German Gerte (rod). In this compound, it functions as a noun specifying the unit of measurement. long: From Old English lang, long (having great linear extent). Of Germanic origin; related to Dutch lang and German lang. In this compound, it functions as an adjective describing the extent.