sexto
/ˈsɛkstəʊ/rare
adjective
Attributive Designating a size or shape of paper produced by folding the original printing sheet to form six leaves, a page of this size or shape, or a book composed of such pages.
Origin
Mid 19th century; earliest use found in Augustus De Morgan (1806–1871), mathematician and historian. From classical Latin sextō, ablative singular of sextus sixth.