Sixty-fourmo is a term used in the bookbinding and printing industry to describe a book or paper size that has been folded 64 times. The term is quite specific, and therefore there are not many synonyms for it. However, another term that can be used to refer to the same size is "64mo," which is a more common abbreviation. Other terms that are used in bookbinding to refer to different paper sizes include duodecimo, quarto, octavo, and folio. Each of these terms describes a book or paper size that has been folded a certain number of times, resulting in a specific number of leaves or pages.