The Collaborative International Dictionary of English v.0.48:

Grewsome \Grew"some\, Gruesome \Grue"some\, a. [From a word akin
   to Dan. gru horror, terror + -some; cf. D. gruwzaam, G.
   grausam. Cf. Grisly.]
   Ugly; frightful.
   [1913 Webster]

         Grewsome sights of war.                  --C. Kingsley.
   [1913 Webster]