Saturn is the outermost of the seven classical planets and traditional ruler of Capricorn and Aquarius, its slow motion linking it to time, limit and old age. Its glyph began as a ligature of kappa and rho, the opening letters of Kronos, the planet's Greek name, marked with a stroke to flag the abbreviation, the same device used to build the signs for Jupiter and several of the other classical planets from Greek initials. In alchemy the identical mark stood for lead, the heaviest and dullest of the seven metals, a fitting counterpart to a planet already associated with slowness and constraint by the time the correspondence between planets and metals had settled into its familiar form by the sixteenth century.
Saturn's weekday is the one clear exception to the general replacement of Roman planetary names by Germanic gods in English: Saturday preserves dies Saturni, Saturn's day, directly and untranslated, because the Anglo-Saxons had no native god judged an adequate match for Saturn, unlike Mars, Mercury, Jupiter and Venus, each swapped for Tiw, Woden, Thor and Frigg in turn. Historians of the calendar generally attribute the exception to Saturn's comparatively minor place in the native Germanic pantheon, which left translators without an obvious local god to substitute, so the Latin name was simply carried across largely unchanged rather than replaced.