dumb

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Lacking the power of speech. Used of animals and inanimate objects.
• adjective Offensive Incapable of using speech; mute. Used of humans.
• adjective Temporarily speechless, as with shock or fear.
• adjective Unwilling to speak; taciturn.
• adjective Not expressed or articulated in sounds or words.
• adjective Nautical Not self-propelling.
• adjective Conspicuously unintelligent; stupid.
• adjective Unintentional; haphazard.
• transitive verb To make silent or dumb.

from The Century Dictionary.

• To become dumb; be silent.
• To make dumb; silence; overpower the sound of.
• Mute; silent; refraining from speech.
• Destitute of the power of speech; unable to utter articulate sounds: as, a deaf and dumb person; the dumb brutes.
• Mute; not accompanied with or emitting speech or sound: as, a dumb show; dumb signs.
• Hence Lacking some usual power, manifestation, characteristic, or accompaniment; destitute of reality in some respect; irregular; simulative: as, dumb ague; dumb craft. See phrases below.
• Dull; stupid; doltish.
• Deficient in clearness or brightness, as a color.
• Synonyms and Mute, etc. See silent.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb obsolete To put to silence.
• adjective Destitute of the power of speech; unable; to utter articulate sounds.
• adjective Not willing to speak; mute; silent; not speaking; not accompanied by words.
• adjective rare Lacking brightness or clearness, as a color.
• adjective See Deaf-mute.
• adjective [U.S.] a form of intermittent fever which has no well-defined “chill.”
• adjective any animal except man; -- usually restricted to a domestic quadruped; -- so called in contradistinction to man, who is a “speaking animal.”
• adjective a cake made in silence by girls on St. Mark's eve, with certain mystic ceremonies, to discover their future husbands.
• adjective (Bot.) a west Indian plant of the Arum family (Dieffenbachia seguina), which, when chewed, causes the tongue to swell, and destroys temporarily the power of speech.
• adjective See under crambo.
• adjective Signs and gestures without words; as, to tell a story in dumb show.
• adjective to confound; to astonish; to render silent by astonishment; or, it may be, to deprive of the power of speech.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb To silence.
• verb transitive To make stupid.
• verb transitive To represent as stupid.
• verb transitive To reduce the intellectual demands of.
• adjective Unable to speak; lacking power of speech.
• adjective informal, pejorative, especially of a person extremely stupid.
• adjective figuratively Pointless, foolish, lacking intellectual content or value.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective temporarily incapable of speaking
• adjective unable to speak because of hereditary deafness
• adjective slow to learn or understand; lacking intellectual acuity
• adjective lacking the power of human speech