megamouth Syllabification: (meg·a·mouth)Pronunciation: /ˈmegəˌmouTH/ (also megamouth shark)Definition of megamouth noun a shark with a very large wide mouth and tiny teeth, first captured in 1976 off the Hawaiian Islands. Megachasma pelagios, the only member of the family Megachasmidae megamouth in other Oxford dictionaries Definition of megamouth in the British & World English dictionary