ironclad

Short definition from Wiktionary

Adjective

1. 1
   Covered with iron, steel, or (loosely) any other tough metal; armor-plated.
2. 2
   Solid or certain; not able to be disputed or questioned; irrefutable.
3. 3
   Rigorous; severe; exacting.
4. 4
   Stubborn; inflexible.

Noun

1. 1
   A ship, vessel, or vehicle with a covering of iron, steel, or (loosely) any other tough metal.
2. 2
   An armor-plated warship, (especially) one preceding the invention of harveyized steel.
3. 3
   A wooden warehouse with an outer skin of corrugated metal.