sextodecimo

Sextodecimo, often abbreviated as 16mo, is a term used in bookbinding and publishing to describe a book's size or format. It refers to a book that has been printed on full sheets of paper, which are then folded three times to create sixteen leaves, or thirty-two pages. This results in a book that is smaller and more compact than those printed in larger formats like folio or quarto.

The term "sextodecimo" is derived from Latin, combining "sex" meaning six and "decimus" meaning tenth, although the exact etymology is somewhat unclear. It is part of a series of terms used to describe book sizes based on the number of leaves created by folding a single sheet of paper. For example, an octavo (8vo) is created by folding a sheet three times to create eight leaves, while a duodecimo (12mo) creates twelve leaves.

Sextodecimo books are typically small, often measuring around 5 to 6 inches in height and width. They were particularly popular during the 16th and 17th centuries, as the smaller size made them more portable and affordable. This format was often used for pocket-sized books, such as prayer books, almanacs, and other popular literature.

In modern publishing, the term sextodecimo is less commonly used, as books are often measured in inches or centimeters rather than by the number of leaves. However, the concept of book size and format remains an important aspect of book design and production. Understanding terms like sextodecimo can provide insight into the history and evolution of the book as a physical object.