twenty-fourmo 二十四开
Twenty-fourmo \Twen`ty-four"mo\, a.
Having twenty-four leaves to a sheet; as, a twenty-fourmo
form, book, leaf, size, etc. -- 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[deg].