The compound "twin-screw" is a modern technical term from naval architecture, formed by combining two English words with clear literal meanings. "Twin," with its ancient Germanic roots signifying duality, is paired with "screw," a word whose journey from a Latin term for a sow (perhaps referring to a pig's spiral tusk) evolved through French to denote a helical fastener and, by metaphoric extension, a ship's propeller. The logic of the term is transparently descriptive: it literally denotes a vessel equipped with "two propellers." This compounding follows a common English pattern for creating precise technical adjectives, where the first element specifies a quantity and the second names the key mechanical component.

Structure: twin (two) + screw (propeller) - twin: From Old English twinn (double, twofold), of Germanic origin; related to Old Norse tvinnr (double). Functions as a combining form meaning "consisting of two identical or similar parts." - screw: From Old French escroue (nut, female screw), of uncertain origin, possibly from Latin scrofa (a sow, suggesting the spiral tusk). In this compound, it functions as a noun meaning "a propeller," a specialized nautical sense derived from its spiral form.