The term 'Certain Seabird' can be solved by two crossword solutions: TERN (4 letters) and SOOTYTERN (9 letters). Terns are a group of seabirds that belong to the family Sternidae, which includes around 40 species. They are known for their long, pointed wings and forked tails. The Sooty TERN is a species of TERN that is found in tropical and subtropical regions of the world. It is a medium-sized seabird with a black head, white underparts, and a dark grey back.