[syn: unassailable, unshakable, watertight, bulletproof]
The Collaborative International Dictionary of English v.0.48:
Unassailable \Unassailable\
   See assailable.
WordNet (r) 3.0 (2006):
unassailable
    adj 1: immune to attack; incapable of being tampered with; "an
           impregnable fortress"; "fortifications that made the
           frontier inviolable"; "a secure telephone connection"
           [syn: impregnable, inviolable, secure, strong,
           unassailable, unattackable]
    2: impossible to assail [syn: unassailable, untouchable]
    3: without flaws or loopholes; "an ironclad contract"; "a
       watertight alibi"; "a bulletproof argument" [syn:
       unassailable, unshakable, watertight, bulletproof]
Moby Thesaurus II by Grady Ward, 1.0:
18 Moby Thesaurus words for "unassailable":
   impenetrable, impregnable, incontestable, indomitable,
   inexpugnable, insuperable, invincible, inviolable, invulnerable,
   irresistible, overpowering, overwhelming, resistless, unbeatable,
   unconquerable, unsubduable, unsurmountable, unyielding