dumb

Etymology 1

From Middle English dumb (“silent, speechless, mute, ineffectual”), from Old English dumb (“silent, speechless, mute, unable to speak”), from Proto-West Germanic *dumb, from Proto-Germanic *dumbaz (“dull, dumb”), from Proto-Indo-European *dʰewbʰ- (“to whisk, smoke, darken, obscure”). The senses of stupid, unintellectual, and pointless, which are found regularly since the 19th century only, probably developed under the influence of German dumm and Dutch dom. Just like the English word, these originally meant "lacking the power of speech", but they developed the mentioned senses early on. Cognates Cognate with Scots dumb (“dumb, silent”), North Frisian dom, domme (“dumb, stupid”), West Frisian dom (“dumb, stupid”), Dutch dom (“dumb, stupid”), German dumm (“dumb, stupid”), Danish dum (“stupid”), Swedish dum (“stupid”), Icelandic dumbur (“dumb, mute”). See also deaf.

adj

1. (dated) Unable to speak; lacking power of speech (kept in "deaf, dumb, and blind").
   His younger brother was born dumb, and communicated with sign language.
   We are dumb and we would talk 1884/1/5, “Mighty maiden with a mission”, in W. S. Gilbert (lyrics), Arthur Sullivan (music), Princess Ida, performed by D'Oyly Carte Opera Company, London, page 48
   Deaf and blind and dumb and born to follow / What you need is someone strong to guide you 1992, “Opiate”, performed by Tool
2. (dated) Silent; unaccompanied by words.
   dumb show
   The country people frequently ſay,—How can you treat a poor dumb beaſt ill; and a ſtreſs is very properly laid on the word dumb; for dumb they appear to thoſe who do not obſerve their looks and geſtures; but God, who takes care of every thing, underſtands their language... 1788, Mary Wollstonecraft, chapter 2, in Original Stories from Real Life (Children's literature), London: J. Johnson, published 1796, pages 10–11
   to pierce into the dumb past 1881, John Campbell Shairp, Aspects of Poetry
3. (informal, derogatory, especially of a person) Extremely stupid.
   You are so dumb! You don't even know how to make toast!
4. (figurative) Pointless, foolish, lacking intellectual content or value.
   This is dumb! We're driving in circles! We should have asked for directions an hour ago!
   Brendan had the dumb job of moving boxes from one conveyor belt to another.
5. Lacking brightness or clearness, as a colour.
   Her stern, which was painted of a dumb white or dun color. 1720, Daniel Defoe, The Life, Adventures and Piracies of the Famous Captain Singleton

Etymology 2

From Middle English dumben, from Old English dumbian (more commonly in compound ādumbian (“to become mute or dumb; keep silence; hold one’s peace”)), from Proto-Germanic *dumbijaną, *dumbōną (“to be silent, become dumb”), from Proto-Indo-European *dʰewbʰ- (“to whisk, smoke, darken, obscure”). Cognate with German verdummen (“to become dumb”).

verb

1. (dated) To silence.
   The paralysis of the Northern conscience, the dumbing of the Northern voice, were coming to an end. 1911, Lindsay Swift, William Lloyd Garrison, page 272
2. (transitive) To make stupid.
   I think she's dumbing us down, so we won't be smarter than her. 2003, Angela Calabrese Barton, Teaching Science for Social Justice, page 124
3. (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. 2004, Stephen Oppenheimer, The Real Eve: Modern Man's Journey Out of Africa, page 107
4. (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. 2002, Deborah Meier, In Schools We Trust: Creating Communities of Learning in an Era of Testing, page 126