The Collaborative International Dictionary of English v.0.48:

Sherbet \Sher"bet\, n. [Ar. sherbet, shorbet, sharbat, properly,
   one drink or sip, a draught, beverage, from shariba to drink.
   Cf. Sorbet, Sirup, Shrub a drink.]
   1. A refreshing drink, common in the East, made of the juice
      of some fruit, diluted, sweetened, and flavored in various
      ways; as, orange sherbet; lemon sherbet; raspberry
      sherbet, etc.
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   2. A flavored water ice.
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   3. A preparation of bicarbonate of soda, tartaric acid,
      sugar, etc., variously flavored, for making an
      effervescing drink; -- called also sherbet powder.
      [1913 Webster]