The Collaborative International Dictionary of English v.0.48:

Felicity \Fe*lic"i*ty\, n.; pl. Felicities. [OE. felicite, F.
   f['e]licit['e], fr. L. felicitas, fr. felix, -icis, happy,
   fruitful; akin to fetus.]
   1. The state of being happy; blessedness; blissfulness;
      enjoyment of good.
      [1913 Webster]

            Our own felicity we make or find.     --Johnson.
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            Finally, after this life, to attain everlasting joy
            and felicity.                         --Book of
                                                  Common Prayer.
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   2. That which promotes happiness; a successful or gratifying
      event; prosperity; blessing.
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            the felicities of her wonderful reign. --Atterbury.
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   3. A pleasing faculty or accomplishment; as, felicity in
      painting portraits, or in writing or talking. "Felicity of
      expression." --Bp. Warburton.

   Syn: Happiness; bliss; beatitude; blessedness; blissfulness.
        See Happiness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

felicity
    n 1: pleasing and appropriate manner or style (especially manner
         or style of expression) [syn: felicity, felicitousness]
         [ant: infelicity]
    2: state of well-being characterized by emotions ranging from
       contentment to intense joy [syn: happiness, felicity]
       [ant: unhappiness]