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n. pl. quar·tos
1. The page size obtained by folding a whole sheet into four leaves.
2. A book composed of pages of this size.
[Short for Middle English (in) quarto, (in) the fourth part (of a sheet), from Medieval Latin (in) quārtō, from Latin, ablative of quārtus, fourth; see kwetwer- in the Appendix of Indo-European roots.]
n, pl -tos
1. (Printing, Lithography & Bookbinding) a book size resulting from folding a sheet of paper, usually crown or demy, into four leaves or eight pages, each one quarter the size of the sheet. Often written: 4to or 4°
2. (Printing, Lithography & Bookbinding) (formerly) a size of cut paper 10 in. by 8 in. (25.4 cm by 20.3 cm)
[C16: from New Latin phrase in quartō in quarter]
n., pl. -tos,
1. a book size of about 9½x 12 in. (24 x 30 cm), determined by folding printed sheets twice to form four leaves or eight pages. Symbol: 4to, 4°
2. a book of this size.adj.
3. bound in quarto.
[1580–90; short for New Latin in quārtō in fourth (Latin quārtō, abl. singular of quartus fourth)]