n. & adj.
--n. (pl. -os)
1. a leaf of paper etc., esp. one numbered only on the front.
2 a leaf-number of a book.
3 a sheet of paper folded once making two leaves of a book.
4 a book made of such sheets.
--adj. (of a book) made of folios, of the largest size.
Phrases and idioms:
in folio made of folios.
Etymology: L, ablat. of folium leaf, on leaf (as specified)