The term 'graceful aquatic bird' can be summarized by two crossword solutions: SWAN (4 letters) and TERN (4 letters). Swans are large waterbirds with long necks, webbed feet, and a graceful gliding flight. They are found in temperate and subarctic regions of the Northern Hemisphere. Terns are smaller birds with long wings, short legs, and a pointed bill. They are found in coastal areas and inland wetlands around the world. Both swans and terns are graceful aquatic birds.