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.] |
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