saturnine

saturnine \SAT-uhr-nyn\, adjective:

1. Born under or being under the astrological influence of the planet Saturn.
2. Gloomy or sullen in disposition.
3. Having a sardonic or bitter aspect.

His saturnine spirit appealed to younger bohemians who were anxious to make idols of an earlier generation's tormented souls, but even so, it cannot have been easy for Rothko always to be the pessimist among the optimists.
-- Jed Perl, review of Mark Rothko: A Biography by James E.B. Breslin, New Republic, January 24, 1994

A saturnine prison guard sits and broods -- and every now and then, gets up and shoots an unseen prisoner.
-- John Walsh, review of The Silence Between Two Thoughts, Independent, June 11, 2004

This captures perfectly the tone of his writing: saturnine, droll, with a fascinating, deliberate bureaucratic dowdiness.
-- Andrew Martin, "Class conscious", New Statesman, November 13, 2000

Saturnine comes from Saturn, in Medieval times believed to be the most remote planet from the Sun and thus coldest and slowest in its revolution.