definition of “dumb” dumb - Definition from the Merriam-Webster Online Dictionary dumb - Definition from the Merriam-Webster Online Dictionary http://www.merriam-webster.com/dictionary/dumb http://www.merriam-webster.com/dictionary/dumb http://www.merriam-webster.com/dictionary/dumb dumb - Definition from the Merriam-Webster Online Dictionary lacking the ability to speak