epenthesis
noun
                                                                                                                            
                                                            epen·the·sis
                    
                                                                                                              
                                                                                                                                  i-ˈpen(t)-thə-səs 
                                                                                                                              
            e-
                                                      
                                                          
            
               plural epentheses
                                        i-ˈpen(t)-thə-ˌsēz 
                                    
    e-
    
            
        
                                
              
          
                                                      : the insertion or development of a sound or letter in the body of a word (such as \ə\ in \ˈa-thə-ˌlēt\ athlete)                                      
                
                    
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  Merriam-Webster unabridged




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