Etymology
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pig iron (n.)

"iron in pigs," as it comes from a blast furnace, iron that has been run while molten into a mold in sand, 1660s; see pig (n.2) + iron (n.).

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cast-iron (n.)

1660s, cast iron, from iron (n.) + cast (adj.) "made by melting and being left to harden in a mold" (1530s), past-participle adjective from cast (v.) in its 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, "made of cast-iron;" figurative sense of "inflexible, unyielding" is from 1830.

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