1. (n.) A book of the size of the fourth of sheet of printing paper whose pages are made by folding a sheet of paper twice\; in present usage, a book of a square or nearly square form, and usually of large size.

crown duodecimo eighteenmo farthing folio fourth fourth part imperial medium octavo octodecimo one-fourth quart quarter quartern royal sextodecimo sixteenmo super twelvemo twenty-five cents twenty-five percent two bits