The Collaborative International Dictionary of English v.0.48:

Button \But"ton\, n. [OE. boton, botoun, F. bouton button, bud,
   prop. something pushing out, fr. bouter to push. See Butt
   an end.]
   1. A knob; a small ball; a small, roundish mass.
      [1913 Webster]

   2. A catch, of various forms and materials, used to fasten
      together the different parts of dress, by being attached
      to one part, and passing through a slit, called a
      buttonhole, in the other; -- used also for ornament.
      [1913 Webster]

   3. A bud; a germ of a plant. --Shak.
      [1913 Webster]

   4. A piece of wood or metal, usually flat and elongated,
      turning on a nail or screw, to fasten something, as a
      door.
      [1913 Webster]

   5. A globule of metal remaining on an assay cupel or in a
      crucible, after fusion.
      [1913 Webster]

   Button hook, a hook for catching a button and drawing it
      through a buttonhole, as in buttoning boots and gloves.

   Button shell (Zool.), a small, univalve marine shell of the
      genus Rotella.

   Button snakeroot. (Bot.)
      (a) The American composite genus Liatris, having rounded
          buttonlike heads of flowers.
      (b) An American umbelliferous plant with rigid, narrow
          leaves, and flowers in dense heads.

   Button tree (Bot.), a genus of trees (Conocarpus),
      furnishing durable timber, mostly natives of the West
      Indies.

   To hold by the button, to detain in conversation to
      weariness; to bore; to buttonhole.
      [1913 Webster]

WordNet (r) 3.0 (2006):

button tree
    n 1: evergreen tree or shrub with fruit resembling buttons and
         yielding heavy hard compact wood [syn: button tree,
         button mangrove, Conocarpus erectus]