Definition of unbreachable
: not able to be entered, penetrated, or crossed : impossible to breach a seemingly unbreachable divide unbreachable computer networks The four-minute mile and the 10-second 100-meter dash were once deemed unbreachable barriers. — Carlos Lozada
First Known Use of unbreachable
Seen and Heard
What made you want to look up unbreachable? Please tell us where you read or heard it (including the quote, if possible).