The Collaborative International Dictionary of English v.0.48:

Sentimental \Sen`ti*men"tal\, a. [Cf. F. sentimental.]
   1. Having, expressing, or containing a sentiment or
      sentiments; abounding with moral reflections; containing a
      moral reflection; didactic. [Obsoles.]
      [1913 Webster]

            Nay, ev'n each moral sentimental stroke,
            Where not the character, but poet, spoke,
            He lopped, as foreign to his chaste design,
            Nor spared a useless, though a golden line.
                                                  --Whitehead.
      [1913 Webster]

   2. Inclined to sentiment; having an excess of sentiment or
      sensibility; indulging the sensibilities for their own
      sake; artificially or affectedly tender; -- often in a
      reproachful sense.
      [1913 Webster]

            A sentimental mind is rather prone to overwrought
            feeling and exaggerated tenderness.   --Whately.
      [1913 Webster]

   3. Addressed or pleasing to the emotions only, usually to the
      weaker and the unregulated emotions.
      [1913 Webster]

   Syn: Romantic.

   Usage: Sentimental, Romantic. Sentimental usually
          describes an error or excess of the sensibilities;
          romantic, a vice of the imagination. The votary of the
          former gives indulgence to his sensibilities for the
          mere luxury of their excitement; the votary of the
          latter allows his imagination to rove for the pleasure
          of creating scenes of ideal enjoiment. "Perhaps there
          is no less danger in works called sentimental. They
          attack the heart more successfully, because more
          cautiously." --V. Knox. "I can not but look on an
          indifferency of mind, as to the good or evil things of
          this life, as a mere romantic fancy of such who would
          be thought to be much wiser than they ever were, or
          could be." --Bp. Stillingfleet.
          [1913 Webster]

WordNet (r) 3.0 (2006):

sentimental
    adj 1: given to or marked by sentiment or sentimentality
    2: effusively or insincerely emotional; "a bathetic novel";
       "maudlin expressions of sympathy"; "mushy effusiveness"; "a
       schmaltzy song"; "sentimental soap operas"; "slushy poetry"
       [syn: bathetic, drippy, hokey, maudlin, mawkish,
       kitschy, mushy, schmaltzy, schmalzy, sentimental,
       soppy, soupy, slushy]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "sentimental":
   adoring, affectionate, apish, asinine, bathetic, batty, beery,
   befooled, beguiled, besotted, brainless, buffoonish, cloying,
   cockeyed, compassionate, conjugal, corny, crazy, credulous, daffy,
   daft, dazed, demonstrative, devoted, dizzy, doting, dreamy, drippy,
   dumb, emotional, faithful, fatuitous, fatuous, filial, flaky, fond,
   fool, foolheaded, foolish, fuddled, futile, gaga, gooey, goofy,
   gulled, gushing, gushy, husbandly, icky, idiotic, imbecile, inane,
   inept, infatuated, insane, insipid, jejune, kooky, languishing,
   loony, lovelorn, lovesick, lovesome, loving, mad, maternal,
   maudlin, mawkish, melting, moist, moonstruck, moronic, mushy,
   namby-pamby, nauseating, nostalgic, nostomanic, nutty,
   oversentimental, oversentimentalized, parental, passionate,
   paternal, romantic, saccharine, sappy, schmaltzy, schoolgirlish,
   screwy, senseless, sentimentalized, sickening, silly, simpering,
   sloppy, slushy, soft, soppy, soupy, sticky, stupid, sweet,
   sympathetic, syrupy, tacky, tear-jerking, tearful, teary, tender,
   thoughtless, uxorious, vapid, wacky, warm-hearted, weepy, wet,
   wifely, witless, yucky