cast iron (n.) Look up cast iron at Dictionary.com
1660s, from cast (past participle adjective) "made by melting and being left to harden in a mold" (1530s), from past participle of cast (v.) in sense "to throw something in a particular way" (c.1300), especially "form metal into a shape by pouring it molten" (1510s). From 1690s as an adjective, cast-iron.