mo

   1. see month

   2. a "unit" traditionally used in printing to describe the page size of a book or other publication. In traditional printing, large sheets are printed, folded, and then cut to manufacture the book. After the cut is made, the sheet has been divided into a certain number of "leaves." Each leaf, folded at the spine of the book, comprises two pages front and back. When sheets were cut to form 4, 8, or 12 leaves, the resulting pages were described as quarto (4to), octavo (8vo) or duodecimo (12mo), respectively. Later, the suffix -mo from duodecimo was made into a suffix that can be attached to any number to indicate the number of leaves per sheet; thus 16mo indicates 16 leaves per sheet. Link: book sizes, from Bookbinding and the Conservation of Books, by Matt T. Roberts and Don Etherington, posted by Stanford University.