The Collaborative International Dictionary of English v.0.48:

Leaf \Leaf\ (l[=e]f), n.; pl. Leaves (l[=e]vz). [OE. leef,
   lef, leaf, AS. le['a]f; akin to S. l[=o]f, OFries. laf, D.
   loof foliage, G. laub, OHG. loub leaf, foliage, Icel. lauf,
   Sw. l["o]f, Dan. l["o]v, Goth. laufs; cf. Lith. lapas. Cf.
   Lodge.]
   1. (Bot.) 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]

   Note: 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. (Bot.) 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]

   Note: 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; as:
      (a) A part of a book or folded sheet containing two pages
          upon its opposite sides.
      (b) A side, division, or part, that slides or is hinged,
          as of window shutters, folding doors, etc.
      (c) The movable side of a table.
      (d) A very thin plate; as, gold leaf.
      (e) A portion of fat lying in a separate fold or layer.
      (f) One of the teeth of a pinion, especially when small.
          [1913 Webster]

   Leaf beetle (Zool.), any beetle which feeds upon leaves;
      esp., any species of the family Chrysomelid[ae], as the
      potato beetle and helmet beetle.

   Leaf bridge, a draw-bridge having a platform or leaf which
      swings vertically on hinges.

   Leaf bud (Bot.), a bud which develops into leaves or a
      leafy branch.

   Leaf butterfly (Zool.), any butterfly which, in the form
      and colors of its wings, resembles the leaves of plants
      upon which it rests; esp., butterflies of the genus
      Kallima, found in Southern Asia and the East Indies.

   Leaf crumpler (Zool.), a small moth (Phycis indigenella),
      the larva of which feeds upon leaves of the apple tree,
      and forms its nest by crumpling and fastening leaves
      together in clusters.

   Leaf fat, the fat which lies in leaves or layers within the
      body of an animal.

   Leaf flea (Zool.), a jumping plant louse of the family
      Psyllid[ae].

   Leaf frog (Zool.), any tree frog of the genus
      Phyllomedusa.

   Leaf green.(Bot.) See Chlorophyll.

   Leaf hopper (Zool.), any small jumping hemipterous insect
      of the genus Tettigonia, and allied genera. They live
      upon the leaves and twigs of plants. See Live hopper.

   Leaf insect (Zool.), any one of several genera and species
      of orthopterous insects, esp. of the genus Phyllium, in
      which the wings, and sometimes the legs, resemble leaves
      in color and form. They are common in Southern Asia and
      the East Indies.

   Leaf lard, lard from leaf fat. See under Lard.

   Leaf louse (Zool.), an aphid.

   Leaf metal, metal in thin leaves, as gold, silver, or tin.


   Leaf miner (Zool.), any one of various small lepidopterous
      and dipterous insects, which, in the larval stages, burrow
      in and eat the parenchyma of leaves; as, the pear-tree
      leaf miner (Lithocolletis geminatella).

   Leaf notcher (Zool.), a pale bluish green beetle (Artipus
      Floridanus), which, in Florida, eats the edges of the
      leaves of orange trees.

   Leaf roller (Zool.), See leaf roller in the vocabulary.


   Leaf scar (Bot.), the cicatrix on a stem whence a leaf has
      fallen.

   Leaf sewer (Zool.), a tortricid moth, whose caterpillar
      makes a nest by rolling up a leaf and fastening the edges
      together with silk, as if sewn; esp., Phoxopteris
      nubeculana, which feeds upon the apple tree.

   Leaf sight, a hinged sight on a firearm, which can be
      raised or folded down.

   Leaf trace (Bot.), one or more fibrovascular bundles, which
      may be traced down an endogenous stem from the base of a
      leaf.

   Leaf tier (Zool.), a tortricid moth whose larva makes a
      nest by fastening the edges of a leaf together with silk;
      esp., Teras cinderella, found on the apple tree.

   Leaf valve, a valve which moves on a hinge.

   Leaf wasp (Zool.), a sawfly.

   To turn over a new leaf, to make a radical change for the
      better in one's way of living or doing. [Colloq.]
      [1913 Webster]

            They were both determined to turn over a new leaf.
                                                  --Richardson.
      [1913 Webster] Leaf