adjective. 
                    In the shape of a half-moon, i.e. semicircular.
                  
                
                  
                    noun. 
                    A fortification constructed beyond the main ditch of a fortress, and in front of the curtain between two bastions, intended to defend the curtain; a ravelin.
                  
                
                  
                    noun. 
                    A crescentic mass of granular protoplasm present in the salivary glands.