rock elm

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An elm (Ulmus thomasii) of eastern North America, having corky branches and hard durable wood.
• noun The wood of this tree.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun large ornamental tree with graceful gradually spreading branches common in eastern North America
• noun tall widely distributed elm of eastern North America