What is "vigesimo-quarto"

Vigesimo-quarto \Vi*ges"i*mo-quar"to\, n.; pl. -tos. A book composed of sheets each of which is folded into twenty-four leaves; hence, indicating more or less definitely a size of book so made; -- usually written 24mo, or 24[deg].

Vigesimo-quarto \Vi*ges"i*mo-quar"to\, a. [L. vigesimus quartus twenty-fourth. Cf. Duodecimo.] Having twenty-four leaves to a sheet; as, a vigesimo-quarto form, book, leaf, size, etc.