The Collaborative International Dictionary of English v.0.48:

Saucer \Sau"cer\, n. [F. sauci[`e]re, from sauce. See Sauce.]
   1. A small pan or vessel in which sauce was set on a table.
      [Obs.] --Bacon.
      [1913 Webster]

   2. A small dish, commonly deeper than a plate, in which a cup
      is set at table.
      [1913 Webster]

   3. Something resembling a saucer in shape. Specifically:
      (a) A flat, shallow caisson for raising sunken ships.
      (b) A shallow socket for the pivot of a capstan.
          [1913 Webster]
          [1913 Webster]

WordNet (r) 3.0 (2006):

saucer
    n 1: something with a round shape resembling a flat circular
         plate; "the moon's disk hung in a cloudless sky" [syn:
         disk, disc, saucer]
    2: a small shallow dish for holding a cup at the table
    3: directional antenna consisting of a parabolic reflector for
       microwave or radio frequency radiation [syn: dish, dish
       aerial, dish antenna, saucer]
    4: a disk used in throwing competitions [syn: discus,
       saucer]