impregnable
Concise Oxford English Dictionary © 2008 Oxford University Press:
impregnable/ɪmˈpreɡnəbl/
▶adjective unable to be captured or broken into.
■ unable to be overcome.
– derivatives
impregnability noun,
impregnably adverb.
impregnability noun,
impregnably adverb.
'impregnable' also found in these Oxford entries:

