The Collaborative International Dictionary of English v.0.48:

Shittim \Shit"tim\, Shittim wood \Shit"tim wood`\, n.
   The wood of the shittah tree.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shittim
    n 1: shrubby thorny deciduous tree of southeastern United States
         with white flowers and small black drupaceous fruit [syn:
         southern buckthorn, shittimwood, shittim, mock
         orange, Bumelia lycioides]

Easton's 1897 Bible Dictionary:

Shittim
   acacias, also called "Abel-shittim" (Num. 33:49), a plain or
   valley in the land of Moab where the Israelites were encamped
   after their two victories over Sihon and Og, at the close of
   their desert wanderings, and from which Joshua sent forth two
   spies (q.v.) "secretly" to "view" the land and Jericho (Josh.
   2:1).


Hitchcock's Bible Names Dictionary (late 1800's):

Shittim, thorns