1
[ adjective ] impossible to assail

Synonyms

untouchable

Related terms

inviolable

2
[ adjective ] able to withstand attack

Examples

"an impregnable fortress" "fortifications that made the frontier inviolable"

Related terms

invulnerable

3
[ adjective ] without flaws or loopholes

Examples

"an ironclad contract" "a watertight alibi" "a bulletproof argument"

Related terms

incontestable

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