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]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "saucer":
   O, annular muscle, annulus, areola, aureole, chaplet, circle,
   circuit, circumference, circus, closed circle, corona, coronet,
   crown, cycle, diadem, discus, disk, eternal return, fairy ring,
   garland, glory, halo, lasso, logical circle, loop, looplet,
   magic circle, noose, orbit, radius, ring, rondelle, round, roundel,
   sphincter, vicious circle, wheel, wreath