Definitions for "Duodecimo"
Having twelve leaves to a sheet; as, a duodecimo from, book, leaf, size, etc.
A book consisting of sheets each of which is folded into twelve leaves; hence, indicating, more or less definitely, a size of a book; -- usually written 12mo or 12°.
A book format formed by a single sheet folded into twelve sections. editio princeps The first printed edition of a work previously available only in manuscript.