There are several synonyms for the phrase "library unit." Some of the most common synonyms include bookcase, bookshelf, shelving unit, and library shelf. These terms are used to describe a structure that is designed to hold books and other reading materials to keep them organized and easily accessible. Additionally, one may also hear the term "library furniture" which refers to any furniture or fixture that is used in a library setting such as tables, chairs, desk, and lamps. Whatever the term used, the purpose remains the same, to create an organized and inviting space for readers to enjoy and explore the world of literature.