The Collaborative International Dictionary of English v.0.48:

Sombrous \Som"brous\, a. [Cf. Sp. sombroso.]
   Gloomy; somber. "Tall and sombrous pines." --Longfellow.
   [1913 Webster] -- Som"brous*ly, adv. -- Som"brous*ness,
   n.
   [1913 Webster]