indispensable
adjective
                                                                                                                            
                                                            in·dis·pens·able
                    
                                                                                                              
                                                                                                                                  ˌin-di-ˈspen(t)-sə-bəl  
                                                      
                                                          
            1
                    
                                          
              
          
                                                      : absolutely necessary : essential                                      
              
                             
an indispensable member of the staff
                         
                
                    2
                    
                                          
              
          
                                                      : not subject to being set aside or neglected                                      
              
                             
an indispensable obligation
                         
                
                    
                                                      indispensable
                                      noun
                                                                            
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  Merriam-Webster unabridged




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