The compound 'three-piece' is a transparent modern English formation, combining the cardinal number 'three' with the noun 'piece'. The word 'three' descends from the Proto-Indo-European numeral tréyes, a root fundamental to counting across Indo-European languages, evident in Latin tres and Greek treis. 'Piece' entered English via Old French from a probable Celtic source, originally implying a fragment or portion. When combined, these morphemes create a straightforward descriptive term, primarily used in tailoring to denote a set—such as a suit—composed of three coordinated garments, logically extending the core idea of 'three parts' into a specific sartorial classification.

Structure: three (number) + piece (part) - three: From Old English þrīe, of 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. - piece: From Old French piece, of Gaulish origin (perhaps from a Celtic base meaning 'portion'); related to patch. Functions as a noun denoting a distinct part or unit.