Source : Webster's Revised Unabridged Dictionary (1913)

Osage orange \O"sage or"ange\ (Bot.)
   An ornamental tree of the genus {Maclura} ({M. aurantiaca}),
   closely allied to the mulberry ({Morus}); also, its fruit.
   The tree was first found in the country of the Osage Indians,
   and bears a hard and inedible fruit of an orangelike
   appearance. See {Bois d'arc}.

Source : WordNet®

osage orange
     n : small shrubby deciduous yellowwood tree of south central
         United States having spines, glossy dark green leaves and
         an inedible fruit that resembles an orange; its hard
         orange-colored wood used for bows by native Americans;
         frequently planted as boundary hedge [syn: {bow wood}, {mock
         orange}, {Maclura pomifera}]