1.  A colored, usually green, expansion growing from the side of a stem or rootstock, in which the sap for the use of the plant is elaborated under the influence of light; one of the parts of a plant which collectively constitute its foliage. [1913 Webster]
" Such leaves usually consist of a blade, or lamina , supported upon a leafstalk or petiole, which, continued through the blade as the midrib, gives off woody ribs and veins that support the cellular texture. The petiole has usually some sort of an appendage on each side of its base, which is called the stipule. The green parenchyma of the leaf is covered with a thin epiderm pierced with closable microscopic openings, known as stomata." [1913 Webster]

2.  A special organ of vegetation in the form of a lateral outgrowth from the stem, whether appearing as a part of the foliage, or as a cotyledon, a scale, a bract, a spine, or a tendril. [1913 Webster]
" In this view every part of a plant, except the root and the stem, is either a leaf, or is composed of leaves more or less modified and transformed." [1913 Webster]

3.  Something which is like a leaf in being wide and thin and having a flat surface, or in being attached to a larger body by one edge or end; [1913 Webster]
" They were both determined to turn over a new leaf." [1913 Webster]

   To shoot out leaves; to produce leaves; to leave; as, the trees leaf in May. Sir T. Browne. [1913 Webster]

leaf, n. & v.
--n. (pl. leaves)
1 a each of several flattened usu. green structures of a plant, usu. on the side of a stem or branch and the main organ of photosynthesis. b other similar plant structures, e.g. bracts, sepals, and petals (floral leaf).
2 a foliage regarded collectively. b the state of having leaves out (a tree in leaf).
3 the leaves of tobacco or tea.
4 a single thickness of paper, esp. in a book with each side forming a page.
5 a very thin sheet of metal, esp. gold or silver.
6 a the hinged part or flap of a door, shutter, table, etc. b an extra section inserted to extend a table.
--v.
1 intr. put forth leaves.
2 tr. (foll. by through) turn over the pages of (a book etc.).

Idiom:
leaf-green the colour of green leaves. leaf insect any insect of the family Phylliidae, having a flattened body leaflike in appearance. leaf-miner any of various larvae burrowing in leaves, esp. moth caterpillars of the family Gracillariidae. leaf-monkey a langur. leaf-mould soil consisting chiefly of decayed leaves. leaf spring a spring made of strips of metal. leaf-stalk a petiole.

Derivative:
leafage n. leafed adj. (also in comb.). leafless adj. leaflessness n. leaflike adj.

Etymology:
OE leaf f. Gmc

N  booklet, writing, work, volume, tome, opuscule, tract, tractate, livret, brochure, libretto, handbook, codex, manual, pamphlet, enchiridion, circular, publication, chap book, part, issue, number livraison, album, portfolio, periodical, serial, magazine, ephemeris, annual, journal, paper, bill, sheet, broadsheet, leaf, leaflet, fly leaf, page, quire, ream, chapter, section, head, article, paragraph, passage, clause, endpapers, frontispiece, cover, binding, folio, quarto, octavo, duodecimo, sextodecimo, octodecimo, encyclopedia, encompilation, library, bibliotheca, press, definitive work, treatise, comprehensive treatise (dissertation), writer, author, litterateur, essayist, journalism, pen, scribbler, the scribbling race, literary hack, Grub-street writer, writer for the press, gentleman of the press, representative of the press, adjective jerker, diaskeaust, ghost, hack writer, ink slinger, publicist, reporter, penny a liner, editor, subeditor, playwright, poet, bookseller, publisher, bibliopole, bibliopolist, librarian, bookstore, bookshop, bookseller's shop, knowledge of books, bibliography, book learning, among the giant fossils of my past, craignez tout d'un auteur en courroux, for authors nobler palms remain, I lived to write and wrote to live, look in thy heart and write, there is no Past so long as Books shall live, the public mind is the creation of the Master-Writ, volumes that I prize above my dukedom.

N  part, portion, dose, item, particular, aught, any, division, ward, subdivision, section, chapter, clause, count, paragraph, verse, article, passage, sector, segment, fraction, fragment, cantle, frustum, detachment, parcel, piece, lump, bit cut, cutting, chip, chunk, collop, slice, scale, lamina, small part, morsel, particle, installment, dividend, share, debris, odds and ends, oddments, detritus, excerpta, member, limb, lobe, lobule, arm, wing, scion, branch, bough, joint, link, offshoot, ramification, twig, bush, spray, sprig, runner, leaf, leaflet, stump, component part, sarmentum, compartment, department, county, fractional, fragmentary, sectional, aliquot, divided, in compartments, multifid, disconnected, partial, partly, in part, partially, piecemeal, part by part, by by installments, by snatches, by inches, by driblets, bit by bit, inch by inch, foot by foot, drop by drop, in detail, in lots.

N  layer, stratum, strata, course, bed, zone, substratum, substrata, floor, flag, stage, story, tier, slab, escarpment, table, tablet, dess, flagstone, board, plank, trencher, platter, plate, lamina, lamella, sheet, foil, wafer, scale, flake, peel, coat, pellicle, membrane, film, leaf, slice, shive, cut, rasher, shaving, integument, eschar, stratification, scaliness, nest of boxes, coats of an onion, monolayer, bilayer, trilayer, lamellar, lamellated, lamelliform, layered, laminated, laminiferous, micaceous, schistose, schistous, scaly, filmy, membranous, pellicular, flaky, squamous, foliated, foliaceous, stratified, stratiform, tabular, discoid, spathic, spathose, trilamellar, graphitic.

N  vegetable, vegetable kingdom, flora, verdure, plant, tree, shrub, bush, creeper, herb, herbage, grass, annual, perennial, biennial, triennial, exotic, timber, forest, wood, woodlands, timberland, hurst, frith, holt, weald, park, chase, greenwood, brake, grove, copse, coppice, bocage, tope, clump of trees, thicket, spinet, spinney, underwood, brushwood, scrub, boscage, bosk, ceja, chaparal, motte, arboretum, bush, jungle, prairie, heath, heather, fern, bracken, furze, gorse, whin, grass, turf, pasture, pasturage, turbary, sedge, rush, weed, fungus, mushroom, toadstool, lichen, moss, conferva, mold, growth, alfalfa, alfilaria, banyan, blow, blowth, floret, petiole, pin grass, timothy, yam, yew, zinnia, foliage, branch, bough, ramage, stem, tigella, spray, leaf, flower, blossom, bine, flowering plant, timber tree, fruit tree, pulse, legume, vegetable, vegetal, vegetive, vegitous, herbaceous, herbal, botanic, sylvan, silvan, arborary, arboreous, arborescent, arborical, woody, grassy, verdant, verdurous, floral, mossy, lignous, ligneous, wooden, leguminous, vosky, cespitose, turf-like, turfy, endogenous, exogenous, green-robed senators of mighty woods, this is the forest primeval.

abruptly-pinnate leaf, acerate leaf, acuminate leaf, amplexicaul leaf, bay leaf, bible leaf, bijugate leaf, bijugous leaf, bipinnate leaf, birch leaf miner, compound leaf, cordate leaf, crenate leaf, cuneate leaf, decompound leaf, deltoid leaf, dentate leaf, denticulate leaf, elliptic leaf, elongate leaf, emarginate leaf, ensiform leaf, entire leaf, erose leaf, even-pinnate leaf, fig leaf, flannel leaf, floral leaf, four-lined leaf bug, gold leaf, hastate leaf, japanese leaf, lanceolate leaf, leaf beet, leaf beetle, leaf blade, leaf blight, leaf bud, leaf bug, leaf cast, leaf cutter, leaf disease, leaf fat, leaf form, leaf insect, leaf lard, leaf lettuce, leaf miner, leaf mold, leaf mould, leaf mustard, leaf out, leaf roller, leaf scorch, leaf shape, leaf soil, leaf spring, linear leaf, lion's leaf, lobed leaf, lyrate leaf, oak leaf, oak leaf cluster, oblanceolate leaf, oblong leaf, obovate leaf, obtuse leaf, odd-pinnate leaf, orbiculate leaf, ovate leaf, paint leaf, painted leaf, palmate leaf, pandurate leaf, panduriform leaf, parallel-veined leaf, parted leaf, pedate leaf, peltate leaf, perfoliate leaf, pine leaf aphid, pinnate leaf, prickly-edged leaf, quinquefoliate leaf, reniform leaf, runcinate leaf, sagittiform leaf, satin leaf, scale leaf, seed leaf, serrate leaf, simple leaf, spatulate leaf, sumatra leaf, tansy leaf aster, tea leaf, trifoliolate leaf, turn over a new leaf, walking leaf