ironwood

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

• noun Any of numerous trees, such as the hornbeam and the hop hornbeam, that have very hard wood.
• noun The wood of any of these trees.

from The Century Dictionary.

• noun In Polynesia, Casuarina equisetifolia, a littoral tree with jointed leafless branches and very hard and heavy wood: used by the natives for making spears. See horsetail-tree and agoho.
• noun A large tree of the myrtle family, Metrosideros lucida, yielding a very hard, strong, red wood, which is used for ship-building, spokes, hubs, and cross-ties for railways.
• noun One of numerous species of peculiarly hard-wooded trees, belonging to many orders and widely distributed.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) A tree unusually hard, strong, or heavy wood.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable Any of a number of tree species known for having a particularly solid wood.
• noun uncountable The wood of any ironwood tree.

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

• noun exceptionally tough or hard wood of any of a number of ironwood trees
• noun medium-sized hop hornbeam of eastern North America
• noun handsome East Indian evergreen tree often planted as an ornamental for its fragrant white flowers that yield a perfume; source of very heavy hardwood used for railroad ties
• noun a small slow-growing deciduous tree of northern Iran having a low domed shape