The Collaborative International Dictionary of English v.0.48:

Savanna \Sa*van"na\, n. [Of American Indian origin; cf. Sp.
   sabana, F. savane.]
   A tract of level land covered with the vegetable growth
   usually found in a damp soil and warm climate, -- as grass or
   reeds, -- but destitute of trees. [Spelt also savannah.]
   [1913 Webster]

         Savannahs are clear pieces of land without woods.
                                                  --Dampier.
   [1913 Webster]

   Savanna flower (Bot.), a West Indian name for several
      climbing apocyneous plants of the genus Echites.

   Savanna sparrow (Zool.), an American sparrow (Ammodramus
      sandwichensis or Passerculus savanna) of which several
      varieties are found on grassy plains from Alaska to the
      Eastern United States.

   Savanna wattle (Bot.), a name of two West Indian trees of
      the genus Citharexylum.
      [1913 Webster]