leaf (n.) Look up leaf at Dictionary.com
Old English leaf "leaf of a plant, foliage; page of a book, sheet of paper," from Proto-Germanic *laubaz (source also of Old Saxon lof, Old Norse lauf, Old Frisian laf, Dutch loof, Old High German loub, German Laub "foliage, leaves," Gothic laufs "leaf, foliage"), probably from PIE *leub(h)- "to peel off, strip or break off" ((source also of Old Irish luib, "herb," lub-gort "garden;" Albanian labë "rind, cork;" Lithuanian luba "plank, board;" Russian lob "forehead, brow," Czech leb "skull;" Lithuanian luobas "bast," Latvian luobas "peel," Russian lub "bast;" Old Norse lyf "medicinal herbs," Old English lybb "poison; magic").

Related to lodge and lobby; for another PIE root see folio. Extended late 14c. to very thin sheets of metal (especially gold). Compare Lithuanian lapas "leaf," from a root also in Greek lepos "bark," lepein "to peel off." Also applied to flat and relatively broad surfaces, especially of flexible or mounted attachments; meaning "hinged flap on the side of a table" is from 1550s. To turn over a (new) leaf (1590s; 1570s as turn the leaf) "begin a new and better course of life" is a reference to the book sense. Among insects, leaf-hopper is from 1847; leaf-cutter from 1816.
leaf (v.) Look up leaf at Dictionary.com
"to turn over (the pages of a book)," 1660s, from leaf (n.). Meaning "put forth leaves or foliage" is from 1610s. Related: Leafed; leaved; leafing.