The Collaborative International Dictionary of English v.0.48:

Mahogany \Ma*hog"a*ny\, Mahogany tree \Ma*hog"a*ny tree`\, n.
   [From the South American name.]
   1. (Bot.) A large tree of the genus Swietenia (Swietenia
      Mahogoni), found in tropical America.
      [1913 Webster]

   Note: Several other trees, with wood more or less like
         mahogany, are called by this name; as, African mahogany
         (Khaya Senegalensis), Australian mahogany
         (Eucalyptus marginatus), Bastard mahogany (Batonia
         apetala of the West Indies), Indian mahogany (Cedrela
         Toona of Bengal, and trees of the genera Soymida and
         Chukrassia), Madeira mahogany (Persea Indica),
         Mountain mahogany, the black or cherry birch (Betula
         lenta), also the several species of Cercocarpus of
         California and the Rocky Mountains.
         [1913 Webster]

   2. The wood of the Swietenia Mahogoni. It is of a reddish
      brown color, beautifully veined, very hard, and
      susceptible of a fine polish. It is used in the
      manufacture of furniture.
      [1913 Webster]

   3. A table made of mahogany wood. [Colloq.]
      [1913 Webster]

   To be under the mahogany, to be so drunk as to have fallen
      under the table. [Eng.]

   To put one's legs under some one's mahogany, to dine with
      him. [Slang]
      [1913 Webster]

WordNet (r) 3.0 (2006):

mahogany
    n 1: wood of any of various mahogany trees; much used for
         cabinetwork and furniture
    2: any of various tropical timber trees of the family Meliaceae
       especially the genus Swietinia valued for their hard
       yellowish- to reddish-brown wood that is readily worked and
       takes a high polish [syn: mahogany, mahogany tree]
    3: a shade of brown with a tinge of red [syn: reddish brown,
       sepia, burnt sienna, Venetian red, mahogany]