[mass noun](Printing)a size of book page resulting from folding each printed sheet into four leaves (eight pages) (印刷)四开 ■[count noun]a book of this size 四开本书 ■a size of writing paper, 10 in. × 8 in. (254 × 203 mm) 四开书写纸
语源
late 16th cent.: from Latin (in) quarto ('in) the fourth (of a sheet'), ablative of quartus 'fourth'