Oc*ta"vo (?), n.;pl. Octavos (#). [L. 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°.
© Webster 1913.
Oc*ta"vo, a.
Having eight leaves to a sheet; as, an octavo form, book, leaf, size, etc.
© Webster 1913.