cast-iron

The compound 'cast-iron' is a straightforward descriptive term from metallurgy, combining the process 'cast' with the material 'iron'. The verb 'cast', with its core sense of throwing, evolved in English to specifically denote the act of pouring liquid material into a mold to give it shape. When paired with 'iron', the name for one of the strongest known ancient metals, it literally describes iron that has been formed by this casting process. The modern figurative meaning of "unyielding" or "inflexible" is a direct metaphorical extension from the material's renowned hardness and durability.

Structure: cast (formed) + iron (metal) - cast: From Old Norse 'kasta' (to throw). In English, it developed the specific sense of shaping molten metal by pouring it into a mold. - iron: From Old English 'īsern/īren', from Proto-Germanic 'īsarną', likely borrowed from a Celtic source meaning 'holy metal'. It refers to the strong, hard metallic element.