impossible
beyond one
beyond reach
closed forever to
closed to
impenetrable
impervious
impracticable
impractical
inaccessible
infeasible
inoperable
insuperable
insurmountable
lost to
out of reach
too much for
un-come-at-able
unaccessible
unachievable
unapproachable
unavailable
uncompassable
undiscoverable
undoable
uneffectible
unfeasible
ungetatable
ungettable
unnegotiable
unobtainable
unperformable
unprocurable
unreachable
unrealizable
unsecurable
unsurmountable
unworkable
attainable
impregnable
insensible
nonexistent
oblivious
unable
unanswerable
unexplored
unfulfilled
unheard
unimaginable
uninhabitable
unknowable
unreadable
unsatisfied
untenable
valueless
explainable
obtainable
sustainable
trainable
unexplainable
unsustainable