Main entry: inexpugnable, impregnable
Definition: incapable of being overcome, challenged or refuted
Usage: an impregnable argument; impregnable self-confidence
Main entry: conceptive, impregnable
Definition: capable of conceiving
Main entry: inviolable, impregnable, unassailable, unattackable, strong, secure
Definition: immune to attack; incapable of being tampered with
Usage: an impregnable fortress; fortifications that made the frontier inviolable; a secure telephone connection