The compound adjective 'three-masted' is a transparent construction from Modern English elements, describing a definitive feature of a sailing vessel's rigging. Its first element, 'three', originates from the ancient Proto-Indo-European root trei-, which gave rise to the number across Indo-European languages, including the Proto-Germanic þrīz. The second element, 'mast', descends from the Proto-Germanic mastaz, likely related to a word for a long, straight piece of wood. The suffix '-ed' is the productive adjectival ending in English, used to form possessional adjectives from nouns. Thus, the term's logic is entirely literal: it directly denotes a ship 'having three masts', with each morpheme retaining its core meaning from its historical roots into the modern nautical term.

Structure: three (number) + mast (pole) + ed (adjective suffix) - three: From Old English þrīe, þrēo, from Proto-Germanic þrīz, meaning the number after two. - mast: From Old English mæst, meaning a tall pole on a ship to support sails, from Proto-Germanic mastaz. - ed: A suffix forming adjectives from nouns, indicating 'having' or 'provided with', from Old English -ede.