The Collaborative International Dictionary of English v.0.48:

Pea \Pea\, n.; pl. Peas (p[=e]z) or Pease (p[=e]z). [OE.
   pese, fr. AS. pisa, or OF. peis, F. pois; both fr. L. pisum;
   cf. Gr. pi`sos, pi`son. The final s was misunderstood in
   English as a plural ending. Cf. Pease.]
   1. (Bot.) A plant, and its fruit, of the genus Pisum, of
      many varieties, much cultivated for food. It has a
      papilionaceous flower, and the pericarp is a legume,
      popularly called a pod.
      [1913 Webster]

   Note: When a definite number, more than one, is spoken of,
         the plural form peas is used; as, the pod contained
         nine peas; but, in a collective sense, the form pease
         is preferred; as, a bushel of pease; they had pease at
         dinner. This distinction is not always preserved, the
         form peas being used in both senses.
         [1913 Webster]

   2. A name given, especially in the Southern States, to the
      seed of several leguminous plants (species of Dolichos,
      Cicer, Abrus, etc.) esp. those having a scar (hilum)
      of a different color from the rest of the seed.
      [1913 Webster]

   Note: The name pea is given to many leguminous plants more or
         less closely related to the common pea. See the
         Phrases, below.
         [1913 Webster]

   Beach pea (Bot.), a seashore plant, Lathyrus maritimus.


   Black-eyed pea, a West Indian name for Dolichos
      sph[ae]rospermus and its seed.

   Butterfly pea, the American plant Clitoria Mariana,
      having showy blossoms.

   Chick pea. See Chick-pea.

   Egyptian pea. Same as Chick-pea.

   Everlasting pea. See under Everlasting.

   Glory pea. See under Glory, n.

   Hoary pea, any plant of the genus Tephrosia; goat's rue.


   Issue pea, Orris pea. (Med.) See under Issue, and
      Orris.

   Milk pea. (Bot.) See under Milk.

   Pea berry, a kind of a coffee bean or grain which grows
      single, and is round or pea-shaped; often used
      adjectively; as, pea-berry coffee.

   Pea bug. (Zool.) Same as Pea weevil.

   Pea coal, a size of coal smaller than nut coal.

   Pea crab (Zool.), any small crab of the genus
      Pinnotheres, living as a commensal in bivalves; esp.,
      the European species (Pinnotheres pisum) which lives in
      the common mussel and the cockle.

   Pea dove (Zool.), the American ground dove.

   Pea-flower tribe (Bot.), a suborder (Papilionace[ae]) of
      leguminous plants having blossoms essentially like that of
      the pea. --G. Bentham.

   Pea maggot (Zool.), the larva of a European moth (Tortrix
      pisi), which is very destructive to peas.

   Pea ore (Min.), argillaceous oxide of iron, occurring in
      round grains of a size of a pea; pisolitic ore.

   Pea starch, the starch or flour of the common pea, which is
      sometimes used in adulterating wheat flour, pepper, etc.


   Pea tree (Bot.), the name of several leguminous shrubs of
      the genus Caragana, natives of Siberia and China.

   Pea vine. (Bot.)
      (a) Any plant which bears peas.
      (b) A kind of vetch or tare, common in the United States
          (Lathyrus Americana, and other similar species).

   Pea weevil (Zool.), a small weevil (Bruchus pisi) which
      destroys peas by eating out the interior.

   Pigeon pea. (Bot.) See Pigeon pea.

   Sweet pea (Bot.), the annual plant Lathyrus odoratus;
      also, its many-colored, sweet-scented blossoms.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pea tree
    n 1: any plant of the genus Caragana having even-pinnate leaves
         and mostly yellow flowers followed by seeds in a linear pod
         [syn: pea tree, caragana]