unreachable
Concise Oxford English Dictionary © 2008 Oxford University Press:
unreachable/ʌnˈriːtʃəb(ə)l/
▶adjective unable to be reached or contacted.
– derivatives
unreachableness noun,
unreachably adverb.
unreachableness noun,
unreachably adverb.
'unreachable' also found in these Oxford entries:

