unassailable
1. [ adjective ] impossible to assail
Synonyms: untouchable
Related terms: inviolable
2. [ adjective ] able to withstand attack
Synonyms: impregnable strong secure unattackable inviolable
Examples:

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

Related terms: invulnerable
3. [ adjective ] without flaws or loopholes
Synonyms: unshakable watertight bulletproof ironclad
Examples:

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

Related terms: incontestable
Similar spelling:   unassailably
  unscalable
  unsalable
  unsyllabled
  unskilled
  unsolvable
  unclassifiable
  unsyllabic
  unskillful
  unsilenced
  unusualness
  unsaleable