To chase with shouts or outcries.
                                                            
                                                     
                        
                                                
                        
                        
                            To call or shout to; to hail.
                                                            
                                                     
                        
                                                
                        
                        
                            An exclamation to call attention or to encourage one.  Now mostly replaced by hello.
                                                            
                                                     
                        
                                                
                        
                        
                            a shout to attract attention; "he gave a great halloo but no one heard him" 
                                                            
                                                     
                        
                                                
                        
                        
                            urge on with shouts; "halloo the dogs in a hunt" 
                                                            
                                                     
                        
                                                
                        
                        
                            shout `halloo', as when greeting someone or attracting attention