就是字面意思"钢铁下颚"，形容一位拳击手的下巴有很强的抗击打能力。下巴是最容易造成KO的打击部位之一，所以下巴强壮对拳击手来说是个很大的优点。
它的反义词是glass jaw，形容下巴很脆弱的选手。

比喻词，百科能查到。
用“下巴” 比喻拳击手的能力，
他不被打晕条件下忍受创伤的能力。
因此，iron jaw 指他 打烂了也不晕的选手。

IRON JAW
In combat sports such as boxing, kickboxing and mixed martial arts, a fighter's chin is a figurative term that refers to an ability to tolerate physical trauma to the head without being knocked unconscious. The fictional Rocky Balboa character of the Rocky franchise epitomizes the concept of a boxer with a granite chin.