IPA: /ˈaɪərnˌmɑːstər/
KK: /ˈaɪərnˌmɑːstər/
A person or company that produces iron or operates an ironworks facility.
The ironmaster oversaw the production of high-quality iron for various industries.
Ironmaster is formed from "iron" (from Old English "iren", meaning the metal iron) and "master" (from Old English "maegester", meaning one who has control or authority). The word refers to a person who has control or authority over iron production or ironworks.
Think of someone who has control or authority ('master') over the metal iron — that's what an ironmaster is.