The Collaborative International Dictionary of English v.0.48:

Simper \Sim"per\, v. i. [imp. & p. p. Simpered; p. pr. & vb.
   n. Simpering.] [Cf. Norw. semper fine, smart, dial. Dan.
   semper, simper, affected, coy, prudish, OSw. semper one who
   affectedly refrains from eating, Sw. sipp finical, prim, LG.
   sipp.]
   1. To smile in a silly, affected, or conceited manner.
      [1913 Webster]

            Behold yond simpering dame.           --Shak.
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            With a made countenance about her mouth, between
            simpering and smiling.                --ir. P.
                                                  Sidney.
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   2. To glimmer; to twinkle. [Obs.]
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            Yet can I mark how stars above
            Simper and shine.                     --Herbert.
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The Collaborative International Dictionary of English v.0.48:

Simper \Sim"per\, n.
   A constrained, self-conscious smile; an affected, silly
   smile; a smirk.
   [1913 Webster]

         The conscious simper, and the jealous leer. --Pope.
   [1913 Webster]

WordNet (r) 3.0 (2006):

simper
    n 1: a silly self-conscious smile
    v 1: smile affectedly or derisively [syn: smirk, simper]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "simper":
   affected, beam, bridle, bright smile, broad grin, crack a smile,
   ear-to-ear grin, gleaming smile, glowing smile, grin, grinning,
   idiotic grin, mince, mince it, prink, sardonic grin,
   self-conscious, smile, smile brightly, smiling, smirk, stupid grin,
   toothful grin, vapid