pig iron

Meanings

1. A brittle, impure form of iron produced by smelting iron ore which is often shaped into blocks; it is unsuitable for working but suitable for casting, and so is commonly used as an industrial raw material; (countable) a sample of such iron.
2. An iron plate which is hung between a piece of meat and the fire used to cook it to prevent the meat from burning if the fire is too hot.

Etymology

From pig (“animal of the family Suidae, especially the domesticated animal Sus domesticus; oblong block of cast metal (iron or lead)”) + iron. It appears that in early use sow was used to refer to larger blocks of smelted metal and pig smaller ones. From the 17th century, the words were adapted to newer methods of iron smelting, with pig used to describe blocks formed from molten iron served from the central channel (runner) of a pig bed which were said to resemble a litter of piglets nursing from a sow.