Covered with iron, steel, or some metal, armor-plated. / (figuratively) Solid or certain; not able to be disputed or questioned; irrefutable. / (figuratively) Rigorous; severe; exacting.

A metal-plated ship, vessel, or vehicle. / (military) An armor-plated warship.

plural of ironclad

(archaic, military, 19th century to pre-WWI) An armoured combat vehicle, a tank.