The term SLINKY'S SHAPE can be summarized by two crossword solutions: COIL (4 letters) and HELIX (5 letters). A Slinky is a toy made of a helical spring-like metal COIL that can stretch and bounce. It was invented in the 1940s and has become a classic toy for children. The shape of a Slinky is a HELIX, which is a three-dimensional spiral. A HELIX is also known as a COIL, which is a single loop of wire or other material that is wound around itself.