cast iron

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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.

Wiktionary

1. adj. Made of cast iron.
2. adj. Durable; tough; resiliant.
3. adj. Inflexible or without exception.
4. n. A hard and brittle, but strong, alloy of iron, carbon, and silicon, formed by casting in a mould.

GNU Webster's 1913

1. 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.
2. n. an impure variety of iron, containing from three to six percent of carbon, part of which is united with a part of the iron, as a carbide, and the rest is uncombined, as graphite. It there is little free carbon, the product is white iron; if much of the carbon has separated as graphite, it is called gray iron. See also Cast iron, in the Vocabulary.

WordNet 3.0

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