- a book size of about 5 × 7½ inches (13 × 19 centimeters), determined by printing on sheets folded to form 12 leaves or 24 pages. Symbol: 12 mo, 12°
- a book of this size.
- in duodecimo; twelvemo.
- a book size resulting from folding a sheet of paper into twelve leaves
- a book of this size
