The term 'library unit' can be broken down into three parts: VOLUME (6 letters), SHELF (5 letters), and BOOK (4 letters). A VOLUME is a single physical item, such as a BOOK or magazine, that is part of a larger collection. A SHELF is a flat surface used to store items, usually in a library or bookstore. A BOOK is a printed or written work consisting of pages glued or sewn together along one side and bound in covers. Together, these three components make up a library unit, which is a unit of organization in a library.