The Collaborative International Dictionary of English v.0.48:

eggplant \egg"plant`\, egg-plant \egg-plant\, n.
   1. (Bot.) A plant (Solanum Melongena), of East Indian
      origin, allied to the tomato, and bearing a large, glossy,
      edible fruit, shaped somewhat like an egg; mad-apple. It
      is widely cultivated for its fruit, commonly eaten as a
      vegetable.

   Syn: eggplant, aubergine, brinjal, eggplant bush, garden egg,
        mad apple, Solanum melongena.
        [1913 Webster + WordNet 1.5]

   2. The fruit of the eggplant[1].
      [PJC]

WordNet (r) 3.0 (2006):

eggplant
    n 1: egg-shaped vegetable having a shiny skin typically dark
         purple but occasionally white or yellow [syn: eggplant,
         aubergine, mad apple]
    2: hairy upright herb native to southeastern Asia but widely
       cultivated for its large glossy edible fruit commonly used as
       a vegetable [syn: eggplant, aubergine, brinjal,
       eggplant bush, garden egg, mad apple, Solanum
       melongena]