The Collaborative International Dictionary of English v.0.48:

Mangrove \Man"grove\, n. [Malay manggi-manggi.]
   1. (Bot.) The name of one or two trees of the genus
      Rhizophora (Rhizophora Mangle, and Rhizophora
      mucronata, the last doubtfully distinct) inhabiting muddy
      shores of tropical regions, where they spread by emitting
      aerial roots, which fasten in the saline mire and
      eventually become new stems. The seeds also send down a
      strong root while yet attached to the parent plant.
      [1913 Webster]

   Note: The fruit has a ruddy brown shell, and a delicate white
         pulp which is sweet and eatable. The bark is
         astringent, and is used for tanning leather. The black
         and the white mangrove (Avicennia nitida and
         Avicennia tomentosa) have much the same habit.
         [1913 Webster]

   2. (Zool.) The mango fish.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mangrove
    n 1: a tropical tree or shrub bearing fruit that germinates
         while still on the tree and having numerous prop roots that
         eventually form an impenetrable mass and are important in
         land building [syn: mangrove, Rhizophora mangle]