What does "octodecimo" mean?

Octodecimo: Having eighteen leaves to a sheet; as, an octodecimo form, book, leaf, size, etc.

Additional senses

  1. 2.A book composed of sheets each of which is folded into eighteen leaves; hence; indicating more or less definitely a size of book, whose sheets are so folded; -- usually written 18mo or 18º, and called eighteenmo.

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