cast iron

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

• noun A hard, brittle, nonmalleable iron-carbon alloy, cast into shape, containing 2 to 4.5 percent carbon, 0.5 to 3 percent silicon, and lesser amounts of sulfur, manganese, and phosphorus.

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

• Highly carbonized iron, the direct product of the blast furnace; -- used for making castings, and for conversion into wrought iron and steel. It can not be welded or forged, is brittle, and sometimes very hard. Besides carbon, it contains sulphur, phosphorus, silica, etc.

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

• adjective not comparable Made of cast iron.
• adjective Durable; tough; resiliant.
• adjective Inflexible or without exception.
• noun A hard and brittle, but strong, alloy of iron, carbon, and silicon, formed by casting in a mould.

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

• noun an alloy of iron containing so much carbon that it is brittle and so cannot be wrought but must be shaped by casting