slippery elm

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

• noun An elm (Ulmus rubra syn. U. fulva) of eastern North America, having hard wood and mucilaginous, aromatic inner bark.
• noun The powdered inner bark of this tree, used medicinally.

from The Century Dictionary.

• noun The red elm, or moose-elm, Ulmus fulva, of eastern North America.

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

• noun North American elm having rough leaves that are red when opening; yields a hard wood