Source : Webster's Revised Unabridged Dictionary (1913)

Tree \Tree\ (tr[=e]), n. [OE. tree, tre, treo, AS. tre['o],
   tre['o]w, tree, wood; akin to OFries. tr[=e], OS. treo, trio,
   Icel. tr[=e], Dan. tr[ae], Sw. tr["a], tr["a]d, Goth. triu,
   Russ. drevo, W. derw an oak, Ir. darag, darog, Gr. dry^s a
   tree, oak, do`ry a beam, spear shaft, spear, Skr. dru tree,
   wood, d[=a]ru wood. [root]63, 241. Cf. {Dryad}, {Germander},
   {Tar}, n., {Trough}.]
   1. (Bot.) Any perennial woody plant of considerable size
      (usually over twenty feet high) and growing with a single
      trunk.

   Note: The kind of tree referred to, in any particular case,
         is often indicated by a modifying word; as forest tree,
         fruit tree, palm tree, apple tree, pear tree, etc.

   2. Something constructed in the form of, or considered as
      resembling, a tree, consisting of a stem, or stock, and
      branches; as, a genealogical tree.

   3. A piece of timber, or something commonly made of timber;
      -- used in composition, as in axletree, boottree,
      chesstree, crosstree, whiffletree, and the like.

   4. A cross or gallows; as Tyburn tree.

            [Jesus] whom they slew and hanged on a tree. --Acts
                                                  x. 39.

   5. Wood; timber. [Obs.] --Chaucer.

            In a great house ben not only vessels of gold and of
            silver but also of tree and of earth. --Wyclif (2
                                                  Tim. ii. 20).

   6. (Chem.) A mass of crystals, aggregated in arborescent
      forms, obtained by precipitation of a metal from solution.
      See {Lead tree}, under {Lead}.

   {Tree bear} (Zo["o]l.), the raccoon. [Local, U. S.]

   {Tree beetle} (Zo["o]l.) any one of numerous species of
      beetles which feed on the leaves of trees and shrubs, as
      the May beetles, the rose beetle, the rose chafer, and the
      goldsmith beetle.

   {Tree bug} (Zo["o]l.), any one of numerous species of
      hemipterous insects which live upon, and suck the sap of,
      trees and shrubs. They belong to {Arma}, {Pentatoma},
      {Rhaphigaster}, and allied genera.

   {Tree cat} (Zool.), the common paradoxure ({Paradoxurus
      musang}).

   {Tree clover} (Bot.), a tall kind of melilot ({Melilotus
      alba}). See {Melilot}.

   {Tree crab} (Zo["o]l.), the purse crab. See under {Purse}.

   {Tree creeper} (Zo["o]l.), any one of numerous species of
      arboreal creepers belonging to {Certhia}, {Climacteris},
      and allied genera. See {Creeper}, 3.

   {Tree cricket} (Zo["o]l.), a nearly white arboreal American
      cricket ({Ecanthus niv[oe]us}) which is noted for its loud
      stridulation; -- called also {white cricket}.

   {Tree crow} (Zo["o]l.), any one of several species of Old
      World crows belonging to {Crypsirhina} and allied genera,
      intermediate between the true crows and the jays. The tail
      is long, and the bill is curved and without a tooth.

   {Tree dove} (Zo["o]l.) any one of several species of East
      Indian and Asiatic doves belonging to {Macropygia} and
      allied genera. They have long and broad tails, are chiefly
      arboreal in their habits, and feed mainly on fruit.

   {Tree duck} (Zo["o]l.), any one of several species of ducks
      belonging to {Dendrocygna} and allied genera. These ducks
      have a long and slender neck and a long hind toe. They are
      arboreal in their habits, and are found in the tropical
      parts of America, Africa, Asia, and Australia.

   {Tree fern} (Bot.), an arborescent fern having a straight
      trunk, sometimes twenty or twenty-five feet high, or even
      higher, and bearing a cluster of fronds at the top. Most
      of the existing species are tropical.

   {Tree fish} (Zo["o]l.), a California market fish
      ({Sebastichthys serriceps}).

   {Tree frog}. (Zo["o]l.)
      (a) Same as {Tree toad}.
      (b) Any one of numerous species of Old World frogs
          belonging to {Chiromantis}, {Rhacophorus}, and allied
          genera of the family {Ranid[ae]}. Their toes are
          furnished with suckers for adhesion. The flying frog
          (see under {Flying}) is an example.

   {Tree goose} (Zo["o]l.), the bernicle goose.

   {Tree hopper} (Zo["o]l.), any one of numerous species of
      small leaping hemipterous insects which live chiefly on
      the branches and twigs of trees, and injure them by
      sucking the sap. Many of them are very odd in shape, the
      prothorax being often prolonged upward or forward in the
      form of a spine or crest.

   {Tree jobber} (Zo["o]l.), a woodpecker. [Obs.]

   {Tree kangaroo}. (Zo["o]l.) See {Kangaroo}.

   {Tree lark} (Zo["o]l.), the tree pipit. [Prov. Eng.]

   {Tree lizard} (Zo["o]l.), any one of a group of Old World
      arboreal lizards ({Dendrosauria}) comprising the
      chameleons.

   {Tree lobster}. (Zo["o]l.) Same as {Tree crab}, above.

   {Tree louse} (Zo["o]l.), any aphid; a plant louse.

   {Tree moss}. (Bot.)
      (a) Any moss or lichen growing on trees.
      (b) Any species of moss in the form of a miniature tree.
          

   {Tree mouse} (Zo["o]l.), any one of several species of
      African mice of the subfamily {Dendromyin[ae]}. They have
      long claws and habitually live in trees.

   {Tree nymph}, a wood nymph. See {Dryad}.

   {Tree of a saddle}, a saddle frame.

   {Tree of heaven} (Bot.), an ornamental tree ({Ailantus
      glandulosus}) having long, handsome pinnate leaves, and
      greenish flowers of a disagreeable odor.

   {Tree of life} (Bot.), a tree of the genus Thuja; arbor
      vit[ae].

   {Tree onion} (Bot.), a species of garlic ({Allium
      proliferum}) which produces bulbs in place of flowers, or
      among its flowers.

   {Tree oyster} (Zo["o]l.), a small American oyster ({Ostrea
      folium}) which adheres to the roots of the mangrove tree;
      -- called also {raccoon oyster}.

   {Tree pie} (Zo["o]l.), any species of Asiatic birds of the
      genus {Dendrocitta}. The tree pies are allied to the
      magpie.

   {Tree pigeon} (Zo["o]l.), any one of numerous species of
      longwinged arboreal pigeons native of Asia, Africa, and
      Australia, and belonging to {Megaloprepia}, {Carpophaga},
      and allied genera.

   {Tree pipit}. (Zo["o]l.) See under {Pipit}.

   {Tree porcupine} (Zo["o]l.), any one of several species of
      Central and South American arboreal porcupines belonging
      to the genera {Ch[ae]tomys} and {Sphingurus}. They have an
      elongated and somewhat prehensile tail, only four toes on
      the hind feet, and a body covered with short spines mixed
      with bristles. One South American species ({S. villosus})
      is called also {couiy}; another ({S. prehensilis}) is
      called also {c[oe]ndou}.

   {Tree rat} (Zo["o]l.), any one of several species of large
      ratlike West Indian rodents belonging to the genera
      {Capromys} and {Plagiodon}. They are allied to the
      porcupines.

   {Tree serpent} (Zo["o]l.), a tree snake.

   {Tree shrike} (Zo["o]l.), a bush shrike.

   {Tree snake} (Zo["o]l.), any one of numerous species of
      snakes of the genus {Dendrophis}. They live chiefly among
      the branches of trees, and are not venomous.

   {Tree sorrel} (Bot.), a kind of sorrel ({Rumex Lunaria})
      which attains the stature of a small tree, and bears
      greenish flowers. It is found in the Canary Islands and
      Teneriffe.

   {Tree sparrow} (Zo["o]l.) any one of several species of small
      arboreal sparrows, especially the American tree sparrow
      ({Spizella monticola}), and the common European species
      ({Passer montanus}).

   {Tree swallow} (Zo["o]l.), any one of several species of
      swallows of the genus {Hylochelidon} which lay their eggs
      in holes in dead trees. They inhabit Australia and
      adjacent regions. Called also {martin} in Australia.

   {Tree swift} (Zo["o]l.), any one of several species of swifts
      of the genus {Dendrochelidon} which inhabit the East
      Indies and Southern Asia.

   {Tree tiger} (Zo["o]l.), a leopard.

   {Tree toad} (Zo["o]l.), any one of numerous species of
      amphibians belonging to {Hyla} and allied genera of the
      family {Hylid[ae]}. They are related to the common frogs
      and toads, but have the tips of the toes expanded into
      suckers by means of which they cling to the bark and
      leaves of trees. Only one species ({Hyla arborea}) is
      found in Europe, but numerous species occur in America and
      Australia. The common tree toad of the Northern United
      States ({H. versicolor}) is noted for the facility with
      which it changes its colors. Called also {tree frog}. See
      also {Piping frog}, under {Piping}, and {Cricket frog},
      under {Cricket}.

   {Tree warbler} (Zo["o]l.), any one of several species of
      arboreal warblers belonging to {Phylloscopus} and allied
      genera.

   {Tree wool} (Bot.), a fine fiber obtained from the leaves of
      pine trees.

Source : WordNet®

tree fern
     n : any of numerous usually tropical ferns having a thick woody
         stem or caudex and a crown of large fronds; found
         especially in Australia and New Zealand; chiefly of the
         families Cyatheaceae and Marattiaceae but some from
         Polypodiaceae