The Collaborative International Dictionary of English v.0.48:

Sneer \Sneer\, v. i. [imp. & p. p. Sneered; p. pr. & vb. n.
   Sneering.] [OE. sneren, Dan. sn?rre to snarl or grin (like
   a dog); cf. Prov. E. sneer to grin, sner to snort, snert to
   sneer at. See Snore, v. i.]
   1. To show contempt by turning up the nose, or by a
      particular facial expression.
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   2. To inssinuate contempt by a covert expression; to speak
      derisively.
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            I could be content to be a little sneared at.
                                                  --Pope.
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   3. To show mirth awkwardly. [R.] --Tatler.
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   Syn: To scoff; gibe; jeer.

   Usage: Sneer, Scoff, Jeer. The verb to sneer implies to
          cast contempt indirectly or by covert expressions. To
          jeer is stronger, and denotes the use of several
          sarcastic reflections. To scoff is stronger still,
          implying the use of insolent mockery and derision.
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                And sneers as learnedly as they,
                Like females o'er their morning tea. --Swift.
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                Midas, exposed to all their jeers,
                Had lost his art, and kept his ears. --Swift.
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                The fop, with learning at defiance,
                Scoffs at the pedant and science. --Gay.
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