1
                    
                                          
              
          
                                                      : a passage for a current of air (as in a mine or to the lungs)                                      
                
                    
2
                    
                                          
              
          
                                                      : a designated route along which airplanes fly from airport to airport                                      
                
                                
            especially                
          
                                                      : such a route equipped with navigational aids                                      
            
            3
                    
                                          
              
          
                                                      : airline                                      
                
                    
4
                    
                                          
              
          
                                                      : a channel of a designated radio frequency for broadcasting or other radio communication                                      
                
                    
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  Merriam-Webster unabridged




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