The term 'oyster SHELL' can be broken down into two crossword solutions: 'SHUCK' and 'SHELL'. 'SHUCK' is a verb meaning to open the SHELL of an oyster, usually with a knife or other tool. 'SHELL' is a noun referring to the hard outer covering of an oyster. Oysters are mollusks that live in saltwater and have been harvested for centuries for their meat and shells. The shells are often used for decoration, jewelry, and other crafts.