Ex lib is a Latin term that refers to a book that was previously owned by someone else. However, if you are looking for synonyms to describe this concept, there are a few alternatives at your disposal. One common synonym is "previously-owned", which conveys the same idea that the book had a prior owner. Another option is "second-hand", which suggests that the book is not brand new but has been used by someone else before. Additionally, you could use the term "used book" as another synonym for ex lib, indicating that the book has been passed down from its original owner to a new reader.