noun
octavo
ahk-TAY-voh/ɑːkˈteɪvəʊ/
A book format made by folding each sheet into eight leaves.
The printer folds each sheet into eight leaves for an octavo.

Etymology
Latin “eighth” connects the name to a sheet folded into eight leaves. What began as a printer’s description of the folded sheet became the name of the resulting book format.
In context
the form of the modern book each sheet of parchment would yield eight pages of an octavo volume
More examples
- The catalog lists the book's format as octavo.
- An octavo has sixteen pages for every folded sheet.
- The library owns two octavos printed in the same year.
Forms
octavo · octavos