(noun) a gruff or angry utterance (suggestive of the growling of an animal).
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Noun Definition 1
(noun) the sound of growling (as made by animals). Synonyms: growl.
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Noun Definition 2
(verb) to utter or emit low dull rumbling sounds. Synonyms: grumble, growl, rumble. Examples: "He grumbled a rude response." "Stones grumbled down the cliff."