sextoyoudaoicibaDictYouDict[sexto 词源字典]
"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", Mid 19th cent.; earliest use found in Augustus De Morgan (1806–1871), mathematician and historian. From classical Latin sextō, ablative singular of sextus sixth.[sexto etymology, sexto origin, 英语词源]