The Collaborative International Dictionary of English v.0.48:

Pepper \Pep"per\ (p[e^]p"p[~e]r), n. [OE. peper, AS. pipor, L.
   piper, fr. Gr. pe`peri, pi`peri, akin to Skr. pippala,
   pippali.]
   1. A well-known, pungently aromatic condiment, the dried
      berry, either whole or powdered, of the Piper nigrum.
      [1913 Webster]

   Note: Common pepper, or black pepper, is made from the
         whole berry, dried just before maturity; white pepper
         is made from the ripe berry after the outer skin has
         been removed by maceration and friction. It has less of
         the peculiar properties of the plant than the black
         pepper. Pepper is used in medicine as a carminative
         stimulant.
         [1913 Webster]

   2. (Bot.) The plant which yields pepper, an East Indian woody
      climber (Piper nigrum), with ovate leaves and apetalous
      flowers in spikes opposite the leaves. The berries are red
      when ripe. Also, by extension, any one of the several
      hundred species of the genus Piper, widely dispersed
      throughout the tropical and subtropical regions of the
      earth.
      [1913 Webster]

   3. Any plant of the genus Capsicum (of the Solanaceae
      family, which are unrelated to Piper), and its fruit;
      red pepper; chili pepper; as, the bell pepper and the
      jalapeno pepper (both Capsicum annuum) and the
      habanero pepper (Capsicum chinense); . These contain
      varying levels of the substance capsaicin (C18H27O3N),
      which gives the peppers their hot taste. The habanero is
      about 25-50 times hotter than the jalapeno according to a
      scale developed by Wilbur Scoville in 1912. See also
      Capsicum and http://www.chili-pepper-plants.com/.
      [1913 Webster + PJC]

   Note: The term pepper has been extended to various other
         fruits and plants, more or less closely resembling the
         true pepper, esp. to the common varieties of
         Capsicum. See Capsicum, and the Phrases, below.
         [1913 Webster]

   African pepper, the Guinea pepper. See under Guinea.

   Cayenne pepper. See under Cayenne.

   Chinese pepper, the spicy berries of the Xanthoxylum
      piperitum, a species of prickly ash found in China and
      Japan.

   Guinea pepper. See under Guinea, and Capsicum.

   Jamaica pepper. See Allspice.

   Long pepper.
      (a) The spike of berries of Piper longum, an East Indian
          shrub.
      (b) The root of Piper methysticum (syn. Macropiper
          methysticum) of the family Piperaceae. See Kava.


   Malaguetta pepper, or Meleguetta pepper, the aromatic
      seeds of the Amomum Melegueta, an African plant of the
      Ginger family. They are sometimes used to flavor beer,
      etc., under the name of grains of Paradise.

   Red pepper. See Capsicum.

   Sweet pepper bush (Bot.), an American shrub (Clethra
      alnifolia), with racemes of fragrant white flowers; --
      called also white alder.

   Pepper box or Pepper caster, a small box or bottle, with
      a perforated lid, used for sprinkling ground pepper on
      food, etc.

   Pepper corn. See in the Vocabulary.

   Pepper elder (Bot.), a West Indian name of several plants
      of the Pepper family, species of Piper and Peperomia.


   Pepper moth (Zool.), a European moth (Biston betularia)
      having white wings covered with small black specks.

   Pepper pot, a mucilaginous soup or stew of vegetables and
      cassareep, much esteemed in the West Indies.

   Pepper root. (Bot.). See Coralwort.

   pepper sauce, a condiment for the table, made of small red
      peppers steeped in vinegar.

   Pepper tree (Bot.), an aromatic tree (Drimys axillaris)
      of the Magnolia family, common in New Zealand. See
      Peruvian mastic tree, under Mastic.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Capsicum \Cap"si*cum\ (k[a^]p"s[i^]*k[u^]m), n. [NL., fr. L.
   capsa box, chest.] (Bot.)
   A genus of plants of many species, producing capsules or dry
   berries of various forms, which have an exceedingly pungent,
   biting taste, and when ground form the red or Cayenne pepper
   of commerce.
   [1913 Webster]

   Note: The most important species are Capsicum baccatum or
         bird pepper, Capsicum fastigiatum or chili pepper,
         Capsicum frutescens or spur pepper (from which
         tabasco is obtained), Capsicum chinense, which
         includes the fiery-hot habanero pepper, and Capsicum
         annuum or Guinea pepper, which includes the bell
         pepper, the jalapeno pepper, the cayenne pepper, and
         other common garden varieties. The fruit is much used,
         both in its green and ripe state, in pickles and in
         cookery. These contain varying levels of the substance
         capsaicin (C18H27O3N), which gives the peppers
         their hot taste. The habanero is about 25-50 times
         hotter than the jalapeno according to a scale developed
         by Wilbur Scoville in 1912. See also Cayenne pepper,
         pepper and http://www.chili-pepper-plants.com/.
         [1913 Webster + PJC]

   3. Any plant of the genus Capsicum (of the Solanaceae
      family, which are unrelated to Piper), and its fruit;
      red pepper; chili pepper; as, the bell pepper and the
      jalapeno pepper (both Capsicum annuum) and the
      habanero pepper (Capsicum chinense); .
      [1913 Webster + PJC]

WordNet (r) 3.0 (2006):

jalapeno pepper
    n 1: hot green or red pepper of southwestern United States and
         Mexico [syn: jalapeno, jalapeno pepper]