covered or cased with iron plates, as a ship for naval warfare; armor-plated.

very rigid or exacting; inflexible; unbreakable

an ironclad contract.

a wooden warship of the middle or late 19th century having iron or steel armor plating.

adjective

abiding , agreed , arranged , certain , changeless , confirmed , definite , determinate , enduring , firm , inflexible , in the bag * , planned , prearranged , settled , stated , stubborn , sure , unalterable , uncompromising , unwavering , immutable , inalterable , invariable , rigid , unchangeable , fixed , irrefutable , permanent , strict , warship