Adjective
invulnerable -
immune to attack; impregnable; "gunners raked the beach from invulnerable positions on the cliffs"
vulnerable capable of being wounded or hurt; "vulnerable parts of the body"
protected guarded from injury or destruction
safe (of an undertaking) secure from risk
secure free from fear or doubt; easy in mind; "he was secure that nothing will be held against him"
unconquerable not capable of being conquered or vanquished or overcome; "a tribute to his courage...and his unconquerable will" - R.E.Danielson; "faced unconquerable difficulties"
air-tight ,
airtight not allowing air or gas to pass in or out
bombproof ,
shellproof able to resist the explosive force of bombs and shells; "bombproof shelter"
defendable ,
defensible capable of being defended
entrenched established firmly and securely; "the entrenched power of the nobility"
unattackable ,
impregnable ,
unassailable ,
inviolable ,
secure ,
strong incapable of being overcome, challenged or refuted; "an impregnable argument" ; "impregnable self-confidence"
tight affected by scarcity and expensive to borrow; "tight money" ; "a tight market"
sheltered protected from danger or bad weather; "a sheltered harbor"
