english
                    
                    
                    
                        1
                           general:: 
                           Phrase(s): knock on something  to rap or tap, often with the knuckles, on something. (See also knock on wood.)  •  She knocked on the door several times.  •  Knock on it again. Maybe she didn’t hear you.
                           
                           
                           
                           
                        
    
                       
                    
                        
                        
                        
                    
 
                    
                        McGrawhill's American Idioms And Phrasal Verbs