dumb

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Lacking the power of speech. Used of animals and inanimate objects.
2. adj. Often Offensive Incapable of using speech; mute. Used of humans. See Usage Note at mute.
3. adj. Temporarily speechless, as with shock or fear: I was dumb with disbelief.
4. adj. Unwilling to speak; taciturn.
5. adj. Not expressed or articulated in sounds or words: dumb resentment.
6. adj. Nautical Not self-propelling.
7. adj. Conspicuously unintelligent; stupid: dumb officials; a dumb decision.
8. adj. Unintentional; haphazard: dumb luck.
9. v. To make silent or dumb.
10. down Slang To rewrite for a less educated or less sophisticated audience.

Century Dictionary and Cyclopedia

1. Mute; silent; refraining from speech.
2. Destitute of the power of speech; unable to utter articulate sounds: as, a deaf and dumb person; the dumb brutes.
3. Mute; not accompanied with or emitting speech or sound: as, a dumb show; dumb signs.
4. 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.
5. Dull; stupid; doltish.
6. Deficient in clearness or brightness, as a color.
7. Synonyms and Mute, etc. See silent.
8. To become dumb; be silent.
9. To make dumb; silence; overpower the sound of.

Wiktionary

1. adj. Unable to speak; lacking power of speech.
2. adj. Of or pertaining to something, especially a person, that is extremely stupid.
3. adj. Pointless, foolish, lacking intellectual content or value.
4. v. To silence.
5. v. To make stupid.
6. v. To represent as stupid.
7. v. To reduce the intellectual demands of.

GNU Webster's 1913

1. adj. Destitute of the power of speech; unable; to utter articulate sounds.
2. adj. Not willing to speak; mute; silent; not speaking; not accompanied by words.
3. adj. Lacking brightness or clearness, as a color.
4. v. To put to silence.

WordNet 3.0

1. adj. temporarily incapable of speaking
2. adj. unable to speak because of hereditary deafness
3. adj. slow to learn or understand; lacking intellectual acuity
4. adj. lacking the power of human speech