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

Octodecimo n. : 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 18¡, and called eighteenmo.

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dictionary, encyclopedia, online dictionary, thesaurus browser, Free Online Dictionary, eighteenth, decim, English dictionary, Late Latin, Indo-European roots, free online English dictionary, Translations, law, explanation, Idioms, senses, page size, sheets.

Defination from the web:
octodecimo in the Online Dictionary. Meaning of octodecimo. Pronunciation of octodecimo. Translations of octodecimo. octodecimo synonyms, octodecimo antonyms. ... 2. A book composed of octodecimo pages. [Late Latin (in) octdecim, (in) an eighteenth, ablative sing. ...