if not
idiom
1
                    
                                          
              
            
                  —used to talk about the negative result or effect of something
You should study. If not, you won't pass the test.
    
                
                    2
                    
                                          
              
            
                  —used to express surprise about meeting someone when it is not expected
So I went to the game and who should I see there if not my old friend Tom!
    
                
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  Merriam-Webster unabridged




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