unutterable
adjective
                                                                                                                            
                                                            un·ut·ter·able
                    
                                                                                                              
                                                                                                                                  ˌən-ˈə-tə-rə-bəl 
                                                      
                                                          
            
                                
              
          
                                                      : being beyond the powers of description : inexpressible                                      
              
                             
an unutterable tragedy
                         
                
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  Merriam-Webster unabridged




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