adj

• (dated) Unable to speak; lacking power of speech.
  "deaf, dumb, and blind"
• (archaic) Not talkative; taciturn or unwilling to speak.
• (dated) Having no input or voice in running things.
  "Life was never a May-game for men; in all times the lot of the dumb-millions born to toil was defaced with manifold sufferings, injustices, heavy burdens, avoidable and unavoidable; not play at all, but hard work that made the sinews sore, and the heart sore."
• (dated, of things, actions, etc.) Unaccompanied by words or speech, silent, wordless.
  "dumb show"

verb

• (transitive, dated) To silence.
  "[…] what I would have spoke Was beastly dumbed by him."
• (transitive) To make stupid.
  "I think she's dumbing us down, so we won't be smarter than her."
• (transitive) To represent as stupid.
  "Bad-mouthing Neanderthals […] is symptomatic of a need to exclude and even demonize. […] I suggest that the unproven dumbing of the Neanderthals is an example of the same cultural preconception."
• (transitive) To reduce the intellectual demands of.
  "The ensuing storm caused the department to lower the bar—amid protests that this was dumbing the test down—so that only 80 percent of urban kids would fail."

adv

• (African-American Vernacular) Very, extremely.
  ""What, you don't like your food?" Russo asks. ¶ "Are you kidding? It's dumb good.""

adj

• (African-American Vernacular, dated) An intensifier expressing contempt; damn, damned.
  "Pap came to stand beside her and watched the two play. "That pup has just plum' fell in love with our Sammy, an' Sam's real took by him," Pap said. "It's a dumb shame, too. I talked to Jim, but he's not of a mind to sell.""