GNU Collaborative International Dictionary of English

Found one definition

1.       
   Grum (grŭm), a. [Cf. Dan. grum furious, Sw. grym, AS. gram, and E. grim, and grumble. √35.]
   1. Morose; severe of countenance; sour; surly; glum; grim. “Nick looked sour and grum.”  Arbuthnof.
   
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   2. Low; deep in the throat; guttural; rumbling; as, “a grum voice”.
   
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