In modern usage, the word tome refers to a large scholarly book, or a single volume of a scholarly work. Usually the word is associated with a particularly large or heavy book, such as a volume of the Oxford English Dictionary or a substantial textbook. Many academic libraries possess a number of weighty examples of tomes. This usage of the word has been documented since 1573. Tome is sometimes used incorrectly to refer to large fiction books.
The word tome originally appeared in the early 1500s to refer to a section or volume of a book. At that time, many books were produced in multiple parts because they tended to be large, heavy, and expensive to make. By purchasing books one volume at a time, collectors could spread the cost out rather than making a bulk expenditure. The word originates from the Latin term “tomus,” which was used to refer to a single volume of a book.
Tomus itself originates from the Greek “tomos,” which means a section or piece cut off. Originally, tomes were released with the intent of being rebound by the owner once he or she had collected all of the volumes in a set. People who specialize in antiquarian books are sometimes frustrated by this, as changes in paper quality and binding from tome to tome could result in damage to other volumes of the book.
Academic books are still released in multiple volumes for much the same reason that they were broken up in the 1500s: they tend to be expensive and difficult to produce. In addition, it can take several decades to complete a scholarly work, so academics will release sections of the book as they are completed to pique interest. This is commonly seen with complex research books such as the Kinsey Report, which was released in multiple volumes between 1948 and 1953.
Tome is also used in a respectful and reverent way, to indicate amazement and awe at the size of a book and its presumably substantial contents. Many academics, especially historians, aspire to produce a tome or two during their lifetime, especially if they intend to retain tenure at a major university. Generally a tome is not considered portable, and would be kept in a library or reading room to be used for reference. People who own substantial tomes are also usually reluctant to lend them out due to their academic value, expense, and size.