In a dumb (meaning silent) manner; mutely or silently(adverb)
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Use "dumbly" in a sentence
"He looked at me dumbly from a face that might have belonged to a man of sixty, so furrowed, tightly drawn, and full of pain it was."
"Now he turned around and looked dumbly at his brother, his mouth agape."
"Mostly people watch Faux Noise and dumbly believe they are actually seeing news instead of knowing it is "entertainment" ala Rupert Murdock. [tabloid crap for the unaware]."