the compound adjective "walnut-size" is a modern english formation that combines two distinct and ancient roots to create a specific unit of measurement. the first element, "walnut", originates from the old english term for the nut of the juglans tree, historically distinguished as the "foreign nut" brought by the romans or celts. the second element, "size", has a complex journey from latin legal and administrative contexts, where assidere (to sit by as an assessor) evolved into a term for an ordinance or fixed measure. the fusion of these elements follows a common english pattern of using a familiar object ("walnut") as a benchmark, modified by the abstract concept of "size" to denote a specific, informally standardized dimension, illustrating the language's tendency to create vivid, comparative descriptors from concrete nouns.

Structure: walnut (nut) + size (dimension) walnut (from old english wealhhnutu, literally "foreign nut", from wealh "foreigner, celt, roman" + hnutu "nut"). size (from old french sise, a shortening of assise "session, regulation, measure", ultimately from latin assidere "to sit beside, assess").