Octavo
Octavo , noun
[Latin in octavo; in in + octavo, abl. of octavus. See Octave.]
A book composed of sheets each of which is folded into eight leaves; hence, indicating more or less definitely a size of book so made; -- usually written 8vo or 8°.
Octavo , adjective
Having eight leaves to a sheet; as, an octavo form, book, leaf, size, etc.