An adjective meaning 'made of iron,' used in the New Testament to describe objects of formidable, unyielding power. In Revelation, the recurring image of an iron rod (Greek sideran rhabdon) portrays the Messiah's absolute sovereign rule (Rev 2:27; 12:5; 19:15), while Acts 12:10 refers to the literal iron gate of Peter's prison. The multilingual evidence is remarkably uniform — Spanish de-hierro, French de-fer, German eisern — all pointing to a single concrete sense: composed of iron, with metaphorical overtones of invincible authority.