The word is a modern English compound adjective formed by directly combining the numeral "three," with ancient Germanic roots traceable to Proto-Indo-European tréyes, and the noun "disc," which entered English via Latin from the Greek diskos, originally meaning a quoit or plate for throwing. The compound logically follows the common English pattern of number-noun combinations (e.g., two-door, five-page) to create a descriptive term. Its specific application to media formats, such as a three-disc album or DVD set, is a 20th-century development, leveraging the established meaning of "disc" for phonograph records and later optical storage media. The construction transparently denotes a set or unit comprised of three discrete disc-shaped objects.

Structure: three (number) + disc (flat circular object) - three: From Old English þrīe, þrēo, 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. - disc: From Latin discus, from Greek diskos 'a discus, plate, dish', from dikein 'to throw'. Functions as the core noun denoting the object.