/ ˈfəʊliəʊ; NAmE ˈfoʊlioʊ/ noun ( pl. -os )
1.
a book made with large sheets of paper, especially as used in early printing
2.
( technical ) a single sheet of paper from a book
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WORD ORIGIN
late Middle English : from Latin , ablative of folium leaf, in medieval Latin used in references to mean on leaf so-and-so . The original sense of in folio (from Italian in foglio ) was in the form of a full-sized sheet or leaf folded once (designating the largest size of book).