- ironclad, brassbound - inflexibly entrenched and unchangeable; "brassbound traditions"; "brassbound party loyalists"; "an ironclad rule"
Antonym: flexible (indirect, via inflexible)
- ironclad, unassailable, unshakable, watertight, bulletproof - without flaws or loopholes; "an ironclad contract"; "a watertight alibi"; "a bulletproof argument"
Antonym: contestable (indirect, via incontestable)