The Collaborative International Dictionary of English v.0.48:

longanberry \longanberry\ n.
   A tree (Dimocarpus longan) of Southeastern Asia to
   Australia grown primarily for its sweet translucent-fleshed
   edible fruit (the longan) resembling litchi nuts; -- it is
   sometimes placed in genera Euphoria or Nephelium.

   Syn: longan, lungen, Dimocarpus longan, Euphoria litchi,
        Nephelium longana.
        [WordNet 1.5]

   2. Asian fruit similar to litchi.

   Syn: dragon's eye.
        [WordNet 1.5]