[C15: from French saturnin, from Medieval Latin sāturnīnus (unattested), from Latin Sāturnus Saturn, with reference to the gloomy influence attributed to the planet Saturn]
"gloomy, morose, sluggish, grave," 1433, lit. "born under the influence of the planet Saturn," from M.E. Saturne (see Saturn). Medieval physiology believed these characteristics to be caused by the astrological influence of the planet Saturn, which was the most remote from
the Sun (in the limited knowledge of the times) and thus coldest and slowest in its revolution.