The term 'THICK TEXTBOOK' can be broken down into two crossword solutions: TOME (4 letters) and THICK (5 letters). A TOME is a large and scholarly book, usually one that is very THICK and heavy. The term is often used to describe books of great importance or value. A THICK textbook is a book that is filled with a lot of information and is usually quite heavy. It is often used in educational settings to provide students with a comprehensive understanding of a subject.