Source : Webster's Revised Unabridged Dictionary (1913)

Locust tree \Lo"cust tree`\ [Etymol. uncertain.] (Bot.)
   A large North American tree of the genus {Robinia} ({R.
   Pseudacacia}), producing large slender racemes of white,
   fragrant, papilionaceous flowers, and often cultivated as an
   ornamental tree. In England it is called {acacia}.

   Note: The name is also applied to other trees of different
         genera, especially to those of the genus {Hymen[ae]a},
         of which {H. Courbaril} is a lofty, spreading tree of
         South America; also to the carob tree ({Ceratonia
         siliqua}), a tree growing in the Mediterranean region.

   {Honey locust tree} (Bot.), a tree of the genus {Gleditschia}
      ) {G. triacanthus}), having pinnate leaves and strong
      branching thorns; -- so called from a sweet pulp found
      between the seeds in the pods. Called also simply {honey
      locust}.

   {Water locust tree} (Bot.), a small swamp tree ({Gleditschia
      monosperma}), of the Southern United States.

Source : WordNet®

locust tree
     n : any of various hard-wooded trees of the family Leguminosae
         [syn: {locust}]