The term 'BOOK WITH STIFF COVERS' can be summarized as 'hardback', which is an 8-letter word. Hardback books are books that have stiff covers, usually made of cardboard covered with cloth, leather, or paper. They are more durable than paperback books and often have a higher quality of printing. Hardback books are often used for reference books, textbooks, and other books that need to be kept in good condition for a long time.