challenging
adjective
                                                                                                                            
                                                            chal·leng·ing
                    
                                                                                                              
                                                                                                                                  ˈcha-lən-jiŋ  
                                                      
                                                          
            1
                    
                                          
              
          
                                                      : arousing competitive interest, thought, or action                                      
              
                             
a challenging course of study
                                       a challenging job
                         
                
                    2
                    
                                          
              
          
                                                      : invitingly provocative : fascinating                                      
              
                             
a challenging personality
                                       challenging questions
                         
                
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  Merriam-Webster unabridged




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