The compound adjective 'three-cornered' is a transparent English formation built from native Germanic and borrowed Romance elements. The numeral 'three' descends directly from the Old English system, tracing back to the common Proto-Indo-European numeral trei-. The noun 'corner' entered Middle English from Anglo-Norman, itself derived from Latin cornu (horn), metaphorically extended to mean a projecting point or angle. The suffix '-ed' is a native Germanic adjectival formative. The word's logic is purely descriptive: it literally means 'provided with three angles'. This literal sense was readily applied metaphorically to any situation, contest, or object involving three distinct parties or points, such as a three-cornered hat or a three-cornered debate.

Structure: three (number) + corner (angle) + ed (adjective suffix) - three: From Old English þrīe, þrēo, of Proto-Germanic origin; related to Dutch drie and German drei, from an Indo-European root shared by Latin tres and Greek treis. Functions as a numerical quantifier. - corner: From Anglo-Norman cornere, from Old French corniere, based on Latin cornu 'horn, projecting point'. Functions as the core noun denoting an angle or projecting part. - ed: A productive English suffix forming adjectives from nouns, indicating 'having' or 'provided with'. Of Germanic origin.