capable of being taken or won by force: a pregnable fortress. open to attack; assailable: a pregnable argument.

What does impregnability mean?

1 : incapable of being taken by assault : unconquerable an impregnable fortress. 2 : unassailable also : impenetrable impregnable walls.

What do unprotected mean?

1 : lacking protection or defense unprotected troops skin unprotected from the sun's rays. 2 : performed without the use of birth control to prevent pregnancy also : performed without the use of a condom to prevent spread of sexually transmitted disease unprotected sex.