1. A book size resulting from folding a sheet of paper eighteen times, or a book of this size.
Usage: printing and bookbinding term; also abbreviated as 18mo

1. Of or relating to a book size of octodecimo; having pages of octodecimo size.
Usage: printing and bookbinding term

Examples

• The rare edition was printed in octodecimo format, making it a compact and portable volume.
• Collectors often seek octodecimo books from the eighteenth century for their historical value.
• The publisher chose an octodecimo size to keep production costs manageable.
• This octodecimo volume fits easily in a coat pocket.
• The library's catalog distinguishes between folio, quarto, and octodecimo editions of the same work.