The term 'KITTEN's Plaything' can be summarized by two crossword solutions: CLEW (4 letters) and YARN (4 letters). A clew is a ball of string or YARN, which is often used as a plaything for kittens. YARN is a type of thread made from natural or synthetic fibers, which is also used as a toy for cats. Both clews and YARN are popular toys for cats, as they provide an opportunity for them to practice their hunting skills.