Twenty-fourmo :: Twenty-fourmo (a.) Having twenty-four leaves to a sheet; as, a twenty-fourmo form, book, leaf, size, etc..
Twenty-fourmo :: Twenty-fourmo (n.) A book composed of sheets, each of which is folded into twenty-four leaves; hence, indicating more or less definitely a size of book whose sheets are so folded; -- usually written 24mo, or 24?..