without flaws or loopholes; "an ironclad contract"; "a watertight alibi"; "a bulletproof argument" inflexibly entrenched and unchangeable; "brassbound traditions"; "brassbound party loyalists"; "an ironclad rule
emphasis If you describe a guarantee or plan as ironclad, you are emphasizing that it has been carefully put together, and that you think it is absolutely certain to work or be successful. ironclad guarantees of safe passage. Type of warship developed in Europe and the U.S. in the mid-19th century, characterized by the iron armour that protected the hull. In the Crimean War (1853-56) the French and British successfully attacked Russian fortifications with "floating batteries," ironclad barges mounting heavy guns. In 1859 the French completed the first iron warship, the Gloire; its iron plates, 4.5 in. (11 cm) thick, were backed by heavy timber. Britain and the U.S. soon followed. Union forces launched armored gunboats on the Mississippi at the start of the American Civil War, and a flotilla captured Fort Henry (1862). The first battle between ironclads was the Battle of the Monitor and Merrimack (1862). Later refinements led to the battleship. See also monitor
A naval vessel having the parts above water covered and protected by iron or steel usually in large plates closely joined and made sufficiently thick and strong to resist heavy shot